Library class to stage via Loader

programming flash
1

I have one swf(loaded.swf) file that contains a class called “GraphicQ”
I load this file to another swf file(Test.swf) and then try to instantiate the GraphicQ class but in this Test.swf
I manage to get the class definition but when I try to add the child to the stage I get this error:

TypeError: Error #2007: Parameter child must be non-null.
at flash.display::DisplayObjectContainer/addChild()

And here is the code:


private var ldr:Loader = new Loader();

//constructor
public function Test()
		{
			var url:String = "loader.swf";
			var urlReq:URLRequest = new URLRequest(url);
			ldr.load(urlReq);
			ldr.contentLoaderInfo.addEventListener(Event.COMPLETE, onComplete);

		}
		
		private function onComplete(event:Event):void {
			var tst:MovieClip = event.target.applicationDomain.getDefinition("GraphicQ") as MovieClip;
			addChild(tst);
		}
}