Предоставленный DisplayObject должен быть дочерним элементом вызывающего объекта

import flash.display.Loader;
import flash.net.URLRequest;
 
stop();
 
var cont:container = new container();
cont.x = 250;
cont.y = 100;
addChild(cont);
 
var ploader:preloader = new preloader();
ploader.visible = false;
cont.addChild(ploader);
 
var url :URLRequest = new URLRequest();
var mcLoader:Loader = new Loader();
mcLoader.x = 250;
mcLoader.y = 100;
addChild(mcLoader);
 
var bac:back = new back();
bac.addEventListener(MouseEvent.CLICK, bacClick);
function bacClick(_event:MouseEvent)
{
    if (this.currentFrame > 6)
      this.prevFrame();
}
setChildIndex(bac, numChildren - 1);
 
mcLoader.contentLoaderInfo.addEventListener(Event.OPEN, loadOpen);
mcLoader.contentLoaderInfo.addEventListener(Event.INIT, loadInit);
mcLoader.contentLoaderInfo.addEventListener(ProgressEvent.PROGRESS, loadProgress);
mcLoader.contentLoaderInfo.addEventListener(Event.COMPLETE, loadComplete);
 
function loadOpen(_event:Event)
{
    ploader.visible = true;
}
 
function loadInit(_event:Event)
{
    (mcLoader.content as MovieClip).stop();
    (mcLoader.content as MovieClip).visible = false;
}
 
function loadProgress(_event:ProgressEvent)
{
    ploader.bar.setProgress(_event.bytesLoaded, _event.bytesTotal);
}
 
function loadComplete(_event:Event)
{
    ploader.visible = false;
    (mcLoader.content as MovieClip).play();
    (mcLoader.content as MovieClip).visible = true;
}
 
var bu1:but1 = new but1();
var bu2:but2 = new but2();
var bu3:but3 = new but3();
var bu4:but4 = new but4();
bac.bu1.addEventListener(MouseEvent.CLICK, bu1Click);
bac.bu2.addEventListener(MouseEvent.CLICK, bu2Click);
bac.bu3.addEventListener(MouseEvent.CLICK, bu3Click);
bac.bu4.addEventListener(MouseEvent.CLICK, bu4Click);
 
function bu1Click(_event:MouseEvent)
{
    mcLoader.unload();
    url.url = "scene1.swf";
    mcLoader.load(url);
}
 
function bu2Click(_event:MouseEvent)
{
    mcLoader.unload();
    url.url = "scene2.swf";
    mcLoader.load(url);
}
 
function bu3Click(_event:MouseEvent)
{
    mcLoader.unload();
    url.url = "scene3.swf";
    mcLoader.load(url);
}
function bu4Click(_event:MouseEvent)
{
    mcLoader.unload();
    url.url = "scene4.swf";
    mcLoader.load(url);
}

setChildIndex(bac, numChildren - 1);

addChildIndex(bac, numChildren - 1);

addChildIndex(bac);