Problem with recursive function & Exception in thread "AWT-EventQueue-0"

Question

I hope that title doesn't put everyone off :)
I have a recursive function that takes in a list of words, and a reference to my current best board. I am kludging the escape function +(tryWords.size() == 0 || mTotalBlankBlocks < 200)+ atm, but eventually it will escape based on whether the current bestBoard meets certain requirements. The function makes iterates through a list of words, and finds all the spaces that the word would fit into the puzzle: getValidSpacedPositions(currentWord); - it then iterates through each of these; placing a word, removing that word from the iterator and the relevant arrayLists and then recurses the function and tries to do the same with the next word etc.
private void computeBoards(ArrayList<Word> tryWords, Board bestBoard) {
     if (tryWords.size() == 0 || mTotalBlankBlocks < 200)
          return;
     for(Iterator<Word> iter = tryWords.iterator(); iter.hasNext(); ){
          Word currentWord = new Word();
          currentWord = iter.next();
          ArrayList<Position> positions = new ArrayList<Position>();
          positions = getValidSpacedPositions(currentWord);
          if (positions.size() != 0)
               iter.remove();
          System.out.println();
          int placedWordsIndex = tryWords.indexOf(currentWord);
          System.out.print(placedWordsIndex+". "+currentWord.getString()+" with "+positions.size()+" positions / ");
          for (Position position : positions) {
               System.out.println("Pos:"+(positions.indexOf(position)+1)+" of "+positions.size()+"  "+position.getX()+","+position.getY()+","+position.getZ());
               int blankBlocksLeft = placeWord(currentWord, position);
               if(blankBlocksLeft != 0)
                    mPlacedWords.add(currentWord);
                    // TODO: Kludge! Fix this.
                    mUnplacedWords.remove(placedWordsIndex+1);
                    System.out.println("adding "+currentWord.getString()+" to added words list");
                    Board compareBoard = new Board(blankBlocksLeft, mPlacedWords.size());
                    if (compareBoard.getPercFilled() > bestBoard.getPercFilled())
                         bestBoard = new Board(blankBlocksLeft, mPlacedWords.size());
                    //**RECURSE**//
                    computeBoards(tryWords, bestBoard);
                    mUnplacedWords.add(currentWord);
                    removeWord(currentWord);
                    System.out.println("removing "+currentWord.getString()+" from added words list");
               else
                    System.out.println("strange error, spaces are there but word cannot place");
          System.out.println("**FINISHED ITERATING POSITIONS");
     System.out.println("**FINISHED ITERATING TRYWORDS");
}This all seems to work fine, but I add it in for completeness because I am not sure if I have done this right. The Exception occurs in the placeWord function which is called from the recursive loop, on the line bolded. For some reason the Arraylist Words seems to initialise with size 1 even though it is a null's when I look at it, (hence all the redundant code here) and I can't seem to test for null either, it seems to works fine for a while until the recursive funciton above has to back up a few iterations, then it crashes with the exception below.
     private int placeWord(Word word, Position originPosition) {
          ArrayList<Word> words = new ArrayList<Word>();
          switch (originPosition.getAxis().getCurrInChar()) {
          case 'x':
               // TODO: This is returning ONE!!!s
               words = mBlockCube[originPosition.getX()][originPosition.getY()][originPosition.getZ()].getWords();
               int tempword1 = mBlockCube[originPosition.getX()][originPosition.getY()][originPosition.getZ()].getWords().size();
               for (int i = 0; i < word.getLength(); i++) {
                    *if (words.get(0) == null)*
                         mBlockCube[originPosition.getX() + i][originPosition.getY()][originPosition.getZ()] = new Block(word, word.getChar(i));
                    else
                         mBlockCube[originPosition.getX() + i][originPosition.getY()][originPosition.getZ()].addWord(word);
               break;
          case 'y':
               words = mBlockCube[originPosition.getX()][originPosition.getY()][originPosition.getZ()].getWords();
               int tempword2 = mBlockCube[originPosition.getX()][originPosition.getY()][originPosition.getZ()].getWords().size();
               for (int i = 0; i < word.getLength(); i++) {
                    *if (words.get(0) == null)*
                         mBlockCube[originPosition.getX()][originPosition.getY() + i][originPosition.getZ()] = new Block(word, word.getChar(i));
                    else
                         mBlockCube[originPosition.getX()][originPosition.getY() + i][originPosition.getZ()].addWord(word);
               break;
          case 'z':
               words = mBlockCube[originPosition.getX()][originPosition.getY()][originPosition.getZ()].getWords();
               int tempword3 = mBlockCube[originPosition.getX()][originPosition.getY()][originPosition.getZ()].getWords().size();
               for (int i = 0; i < word.getLength(); i++) {
                    *if (words.get(0) == null)*
                         mBlockCube[originPosition.getX()][originPosition.getY()][originPosition.getZ() + i] = new Block(word, word.getChar(i));
                    else
                         mBlockCube[originPosition.getX()][originPosition.getY()][originPosition.getZ() + i].addWord(word);
               break;
          mTotalBlankBlocks -= word.getLength();
          word.place(originPosition);
          String wordStr = new String(word.getWord());
          System.out.println("Word Placed: " + wordStr + " on Axis: " + originPosition.getAxis().getCurrInChar() + " at pos: "
                    + originPosition.getX() + "," + originPosition.getY() + "," + originPosition.getZ());
          return mTotalBlankBlocks;
Exception in thread "AWT-EventQueue-0" java.lang.IndexOutOfBoundsException: Index: 0, Size: 0
     at java.util.ArrayList.RangeCheck(Unknown Source)
     at java.util.ArrayList.get(Unknown Source)
     at com.edzillion.crossword.GameCube.placeWord(GameCube.java:189)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:740)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.computeBoards(GameCube.java:763)
     at com.edzillion.crossword.GameCube.generateGameCube2(GameCube.java:667)
     at com.edzillion.crossword.GameCube.<init>(GameCube.java:42)
     at com.edzillion.crossword.Crossword.actionPerformed(Crossword.java:205)
     at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
Any ideas? I've looked up this exception which didn't shed any light...                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       

Answer 1

ArrayList<Word> words = new ArrayList<Word>();See the API Javadoc for ArrayList: this creates an empty ArrayList.
if (words.get(0) == null)This tries to read the first element of the (still empty) array list -> throws IndexOutOFBoundsException
If you want to stick to that logic (I am too lazy to proof-read your whole algorithm, but that should at least unblock you), you should first check whether the list actually contains at least one element:
if (!words.isEmpty()) {...}