removeChild() Issue

programming flash
1

Can someone tell me why I’m getting an error at removeChild?


private function initCourse (e:Event):void {
            Interface._ui.removeEventListener (Event.ADDED_TO_STAGE, initCourse);
            addChild (Interface._pageHolder);

            var progressBar:ProgressBar = new ProgressBar();
            progressBar.source = Interface._pageHolder.contentLoaderInfo;
            progressBar.x = 300;
            progressBar.y = 400;
            addChild (progressBar);

            Interface._pageHolder.load (new URLRequest(externalSWF));
            Interface._pageHolder.name = "pageHolder";
            
            Interface._pageHolder.contentLoaderInfo.addEventListener (Event.COMPLETE, finishLoading);
            function finishLoading (e:Event):void {
                removeChild (progressBar);
                //progressBar = null;
            }

}

ArgumentError: Error #2025: The supplied DisplayObject must be a child of the caller.
at flash.display::DisplayObjectContainer/removeChild()
at MethodInfo-366()