Randome error

Question

I have a gallery with a button inside a movie clip on my stage. When the button i puched it should navigate to another keyframe with the label "frontpage" back on the main timeline.
When I test the movie, the first time i puch the buttom it leads me back to "frontpage" but when I try a 2nd time it jumps back to "frontpage" but comes with this error:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
    at delaneytrager2_fla::gallerytotal_16/clickHandler_back()[delaneytrager2_fla.gallerytotal_1 6::frame1:239]
The AS for the button is as follows:
stage.addEventListener(MouseEvent.CLICK, clickHandler_back);
function clickHandler_back(event:MouseEvent):void{
    if (event.target.name!=null){
        switch(event.target.name) {
            case "back_btn":
            MovieClip(root).gotoAndStop("frontpage2");
            break;
            default:
            trace("defaultbehavior");
Not really sure what to do about this error message..?

Answer 1

this is all the code from frame 1 i imagine it frame 1 inside the movie clip where my gallery is - since it's the only place there is 239 lines.
The button is basicly the back_btn from the post about "gallery name confussion" you just helped me out with. So it's how i can get out of my gallery movieclip and back on the mainstage to a specific frame.
This is all the code on frame1
var galWid:uint=879.95;
var galHei:uint=350;
var galX:Number=200;
var galY:Number=300;
var scale:Number=1.7;
var speed:Number=0.5;
var scrollX:uint=20;
var alignLeft:Boolean=false;
// Disse bliver kun brugt hvis alignLeft er 'true'
// Dete skal angives i ønskede koordinater.
var offsetX:Number = 40;
var offsetY:Number = 160;
import com.greensock.TweenLite;
import com.greensock.OverwriteManager;
import com.greensock.plugins.*;
TweenPlugin.activate([TransformAroundCenterPlugin,AutoAlphaPlugin]);
var loader:URLLoader = new URLLoader();
var images:XML;
var imageArray:Array = new Array();
var imgNum:uint=0;
var imgLen:uint;
var imgX:uint=0;
var curImg:uint;
var exposed:Boolean=false;
OverwriteManager.init(2);
back_btn.x=600
back_btn.y=300
prevBtn.visible=false;
nextBtn.visible=false;
nextBtn.addEventListener(MouseEvent.CLICK, nextImg);
prevBtn.addEventListener(MouseEvent.CLICK, prevImg);
gallery.addEventListener(MouseEvent.MOUSE_MOVE,scrollImage);
gallery.addEventListener(MouseEvent.MOUSE_OUT, offImage);
loader.addEventListener(Event.COMPLETE, setup);
loader.load(new URLRequest("xml/rabitsketch.xml"));
function setup(e:Event):void {
    images=new XML(e.target.data);
    imgLen=images.image.length();
    galMask.width=galWid;
    galMask.height=stage.stageHeight;
    galMask.x=galX;
    galMask.y=stage.stageHeight*0.5;
    gallery.x=galX;
    gallery.y=galY;
    addImage();
function addImage():void {
    var img:imgCon = new imgCon();
    imageArray.push(img);
    img.con.source=images.image[imgNum].src;
    img.con.addEventListener(Event.COMPLETE,comImage);
    img.addEventListener(MouseEvent.CLICK,expImage);
    img.addEventListener(MouseEvent.MOUSE_OVER, onImage);
    function comImage(e:Event):void {
        TweenLite.from(img,0.5,{alpha:0});
        img.con.height=galHei;
        e.target.content.smoothing=true;
        img.con.width=(img.width/img.height)*img.con.height;
        img.x=imgX;
        img.num=imgNum;
        img.des1=images.image[imgNum].des1;
        img.des2=images.image[imgNum].des2;
        imgX+=img.con.width;
        gallery.addChild(img);
        imgNum++;
        if (imgNum<imgLen) {
            addImage();
function scrollImage(Event):void {
    if (gallery.width>galWid) {
        var procent:Number = ((mouseX-galX)/galWid);
        if (procent<0.1) {
            procent=0;
        if (procent>0.9) {
            procent=1;
        TweenLite.to(gallery, scrollX, {x:galX-(gallery.width-galWid)*procent, y:galY});
        TweenLite.to(gallery, scrollX, {x:galX-(gallery.width-galWid)*procent, y:galY});
    } else {
        TweenLite.to(gallery,speed,{y:galY, x:galX});
function onImage(e:MouseEvent):void {
    desTxtSmall.htmlText=e.currentTarget.des1;
function offImage(e:MouseEvent):void{
    desTxtSmall.htmlText='';
function expImage(e:MouseEvent):void {
    curImg=e.currentTarget.num;
    gallery.setChildIndex(imageArray[curImg], gallery.numChildren - 1);
    imageArray[curImg];
    if (! exposed) {
        for (var i=0; i<gallery.numChildren; i++) {
            TweenLite.to(gallery.getChildAt(i),speed,{autoAlpha:0});
        exposed=true;
        toggleBtns();
        gallery.removeEventListener(MouseEvent.MOUSE_MOVE, scrollImage);
        e.currentTarget.removeEventListener(MouseEvent.MOUSE_OUT, hideDes);
        e.currentTarget.removeEventListener(MouseEvent.MOUSE_OVER, showDes);
        e.currentTarget.removeEventListener(MouseEvent.CLICK, expImage);
        e.currentTarget.addEventListener(MouseEvent.CLICK, minImage);
        desTxt.visible=true;
        desTxtSmall.visible=false;
        desTxt.htmlText=e.currentTarget.des2;
        if (alignLeft) {
            TweenLite.to(galMask,0.5,{x:offsetX,width:stage.stageWidth});
            TweenLite.to(gallery, speed,{x:-e.currentTarget.x+offsetX+((e.currentTarget.width*scale-e.currentTarget.width)* 0.5)});
            TweenLite.to(e.currentTarget,speed,{autoAlpha:1, transformAroundCenter:{scaleX:scale, scaleY:scale}, y:-galY+offsetY});
        } else {
            TweenLite.to(galMask,0.5,{x:galX+galWid*0.5-(e.currentTarget.width*0.5*scale),width:stage .stageWidth});
            TweenLite.to(gallery, speed,{x:-e.currentTarget.x-e.currentTarget.width*0.5+(galWid*0.5)+galX});
            TweenLite.to(e.currentTarget,speed,{autoAlpha:1, transformAroundCenter:{scaleX:scale, scaleY:scale}});
function minImage(e:Event):void {
    exposed=false;
    back_btn.x=600
    back_btn.y=300
    prevBtn.visible=false;
    nextBtn.visible=false;
    TweenLite.to(galMask,0.5,{x:galX, width:galWid});
    for (var i=0; i<gallery.numChildren; i++) {
        TweenLite.to(gallery.getChildAt(i),speed,{autoAlpha:1});
    e.currentTarget.removeEventListener(MouseEvent.CLICK, minImage);
    e.currentTarget.addEventListener(MouseEvent.CLICK, expImage);
    gallery.addEventListener(MouseEvent.MOUSE_MOVE, scrollImage);
    desTxt.visible=false;
    desTxtSmall.visible=true;
    //TweenLite.to(desTxt,speed,{x:txtMinX, y:txtMinY});
    TweenLite.to(e.currentTarget,speed,{transformAroundCenter:{scaleX:1, scaleY:1},y:0});
    TweenLite.to(gallery,speed,{y:galY});
    //TweenLite.to(galMas,speed,{height:galHei*scale, width:galWid, y:galY, x:galX});
    scrollImage(null);
function showDes(e:Event):void {
    if (! exposed) {
        desTxt.visible=true;
        desTxt.htmlText=e.target.des1;
function hideDes(e:Event):void {
    if (! exposed) {
        desTxt.visible=false;
function nextImg(Event) {
    if (curImg<imgLen-1) {
        imageArray[curImg].addEventListener(MouseEvent.CLICK, expImage);
        imageArray[curImg].removeEventListener(MouseEvent.CLICK, minImage);
        TweenLite.to(imageArray[curImg],0.5,{transformAroundCenter:{scaleX:1, scaleY:1},autoAlpha:0, y:0});
        var nextImg=imageArray[++curImg];
        gallery.setChildIndex(nextImg, gallery.numChildren - 1);
        nextImg.removeEventListener(MouseEvent.CLICK, expImage);
        nextImg.addEventListener(MouseEvent.CLICK, minImage);
        desTxt.htmlText=nextImg.des2;
        if (alignLeft) {
            TweenLite.to(gallery, speed,{x:-nextImg.x+offsetX+((nextImg.width*scale-nextImg.width)*0.5)});
            TweenLite.to(nextImg,speed,{autoAlpha:1, transformAroundCenter:{scaleX:scale, scaleY:scale}, y:-galY+offsetY});
        } else {
            TweenLite.to(gallery, speed,{x:-nextImg.x-nextImg.width*0.5+(galWid*0.5)+galX});
            TweenLite.to(nextImg,speed,{autoAlpha:1, transformAroundCenter:{scaleX:scale, scaleY:scale}});
        toggleBtns();
function prevImg(Event) {
    if (curImg>0) {
        imageArray[curImg].addEventListener(MouseEvent.CLICK, expImage);
        imageArray[curImg].removeEventListener(MouseEvent.CLICK, minImage);
        TweenLite.to(imageArray[curImg],0.5,{transformAroundCenter:{scaleX:1, scaleY:1},autoAlpha:0,y:0});
        var prevImg=imageArray[--curImg];
        gallery.setChildIndex(prevImg, gallery.numChildren - 1);
        prevImg.removeEventListener(MouseEvent.CLICK, expImage);
        prevImg.addEventListener(MouseEvent.CLICK, minImage);
        desTxt.htmlText=prevImg.des2;
        if (alignLeft) {
            TweenLite.to(gallery, speed,{x:-prevImg.x+offsetX+((prevImg.width*scale-prevImg.width)*0.5)});
            TweenLite.to(prevImg,speed,{autoAlpha:1, transformAroundCenter:{scaleX:scale, scaleY:scale}, y:-galY+offsetY});
        } else {
            TweenLite.to(gallery, speed,{x:-prevImg.x-prevImg.width*0.5+(galWid*0.5)+galX});
            TweenLite.to(prevImg,speed,{autoAlpha:1, transformAroundCenter:{scaleX:scale, scaleY:scale}});
        toggleBtns();
function toggleBtns():void {
    if (curImg>0) {
        prevBtn.visible=true;
    } else {
        prevBtn.visible=false;
    if (curImg<imgLen-1) {
        nextBtn.visible=true;
    } else {
        nextBtn.visible=false;
    back_btn.x=250
    back_btn.y=225
stage.addEventListener(MouseEvent.CLICK, clickHandler_back);
function clickHandler_back(event:MouseEvent):void{
    if (event.target!=null){
        switch(event.target.name) {
            case "back_btn":
            MovieClip(root).gotoAndStop("frontpage2");
            break;
            default:
            trace("defaultbehavior");
stop();