Supplied DisplayObject must be a child of the caller?

1

im getting the following error

ArgumentError: Error #2025: The supplied DisplayObject must be a child of the caller.
at flash.display:isplayObjectContainer/removeChild()
at guide_fla::memb2_13/frame1()
at flash.display::MovieClip/gotoAndStop()
at guide_fla::memb3_14/active()

from this section of code

var mem2:m2 = new m2();
stop();
if(MovieClip(root).c>0){
	this.parent.removeChild(mem2);
}

this.addEventListener(MouseEvent.MOUSE_DOWN, active);
function active (e:MouseEvent):void {
	this.gotoAndStop(2);
	MovieClip(parent).memb1.gotoAndStop(1);
	MovieClip(parent).memb3.gotoAndStop(1);
	MovieClip(parent).memb4.gotoAndStop(1);
	MovieClip(parent).addChild(mem2);
	mem2.x = 280;
	mem2.y = 140;
	var c:int = 0;
	MovieClip(root).c = 1;
}

there is also a variable c on the root timeline.
can anyone tell me why im getting this error?