Problem with loading and unloading external swfs

Question

Hello Forum,
I'm pretty new to as3, and it's giving me a great challenge. I have a large number of captivate files that I want to play inside a simple container built in CS5.5... but switching back and forth between all the movies hogs the memory like crazy, so I need something to clean it up. All code is in a single frame on the main timeline. First, I create the loader:
var FlashLoader:Loader = new Loader();
var flashUrl:URLRequest = new URLRequest("placeholder.swf");
FlashLoader.load(flashUrl);
addChild(FlashLoader);
The actual movies are located via an XML... but as I said the memory problem is huge, so I tried to build something to get rid of that. Ideally, I want the loader to clean up everything and start life anew with a single mouse click, like so:
function _mouseClickHandler2(event:MouseEvent):void {
          FlashLoader.unloadAndStop();
          FlashLoader.parent.removeChild(FlashLoader);
          FlashLoader = null;
          var flashUrl:URLRequest = new URLRequest(event.target.href);
          var FlashLoader:Loader = new Loader();
          addChild(FlashLoader);
          FlashLoader.load(flashUrl);
          FlashLoader.x = 120;
          setChildIndex(FlashLoader,0);
          trace(FlashLoader.parent.numChildren);
//          System.gc();
//          System.gc();
//          try {
//                    new LocalConnection  .connect('gc');
//                    new LocalConnection  .connect('gc');
//          } catch (e: * ) {
//          trace(getMemory ());
//trace(event.target.href);
//trace(event.target.text);
Upon clicking on the menu (and thus switching movies), I get the following error:
TypeError: Error #1009: Cannot access a property or method of a null object reference.
          at Treeview_working_fla::MainTimeline/_mouseClickHandler2()
And this doesn't make sense to me. The FlashLoader is given a placeholder swf at the beginning, so why would the FlashLoader inside the function be recognized as having a null object reference?
Thanks in advance

Answer 1

In my quest to tackle this problem, I've decided to try and isolate the problem, and have made a simple "click to load, click to unload" when I stumbled upon a curious problem. The movie loads fine, and the UNLOAD function upon mouseclick also works perfectly. However, upon clicking again to activate RELOAD, it gives the error "No active security context" and refuses to load the same exact swf with the same exact path that successfully loaded the first time!
import flash.events.MouseEvent;
import flash.display.Loader;
import flash.net.URLRequest;
var FlashLoader:Loader = new Loader();
var flashUrl:URLRequest = new URLRequest("folder/subfolder/movie.swf");
FlashLoader.x = 120;
FlashLoader.load(flashUrl);
stage.addChild(FlashLoader);
stage.addEventListener(MouseEvent.CLICK, UNLOAD);
function UNLOAD(event:MouseEvent) {
          flashUrl = null;
          stage.removeChild(FlashLoader);
          FlashLoader.unloadAndStop();
          stage.removeEventListener(MouseEvent.CLICK, UNLOAD);
          stage.addEventListener(MouseEvent.CLICK, RELOAD);
function RELOAD(event:MouseEvent) {
          var FlashLoader:Loader = new Loader();
          var flashUrl:URLRequest = new URLRequest("folder/subfolder/movie.swf");
          FlashLoader.x = 120;
          FlashLoader.load(flashUrl);
          stage.addChild(FlashLoader);
          stage.removeEventListener(MouseEvent.CLICK, RELOAD);
          stage.addEventListener(MouseEvent.CLICK, UNLOAD);