Photo gallery (using Loader with no xml)

Question

Hello, currently I'm doing a photo gallery.
Inside .fla, only 2 frame:
1st is for my 3 category: A, B, C.
stop();
A.addEventListener(MouseEvent.CLICK, clickSection);
B.addEventListener(MouseEvent.CLICK, clickSection);
C.addEventListener(MouseEvent.CLICK, clickSection);
function clickSection(evt:MouseEvent):void{
    gotoAndStop("gallery");
    loader.unload();
    req = new URLRequest(evt.target.name + "_gallery.swf");
    createLoader();
    loader.load(req);
2nd is to load the swf externally.
var req:URLRequest
var container_mc:MovieClip
var loader:Loader = new Loader();
req = new URLRequest("A.swf");
createLoader();
loader.load(req);
function createLoader():void{
    loader = new Loader();
    loader.contentLoaderInfo.addEventListener(Event.INIT, initListener);
    loader.contentLoaderInfo.addEventListener(Event.COMPLETE, fileLoaded);
function initListener(evt:Event):void{
    addChildAt(loader,1);
function fileLoaded(evt:Event):void{
    container_mc = MovieClip(loader.content);
debug (click the button and it pop this):
RangeError: Error #2006: The supplied index is out of bounds.
    at flash.display::DisplayObjectContainer/addChildAt()
    at main_gallery_fla::MainTimeline/initListener()
any ideas why?

Answer 1

Yes, two... the first being the most important...
1) Learn how to use the help documentation (and Google).  If you look up addChild in the help documents it will define what you need to know to be able to use it.  The same goes for any other element of the AS3 language.  The help documents are a primary tool in learning/using AS3 (or any language).
2) use:  addChild(loader);
I couldn't really follow your description in the first posting, but I would almost expect a flurry of other errors unless I am misinterpretting what you described.  Very often errors get reported in sequence, not all at once.