Scrollbar in loaded swf stops working

1

Hi, sorry if this is a very n00b question but i have a class Scrollbar, which works fine unless I load the swf into another movie.

I get an error on this thing:

public function Scrollbar():void {
scroller.addEventListener(MouseEvent.MOUSE_DOWN, dragScroll);
stage.addEventListener(MouseEvent.MOUSE_UP, stopScroll);			
stage.addEventListener(MouseEvent.MOUSE_WHEEL,mouseWheelHandler);
}

This is the error:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
	at Scrollbar()
	at flash.display::Sprite/constructChildren()
	at flash.display::Sprite()
	at flash.display::MovieClip()
	at sisteprosjekt_fla::MainTimeline()
TypeError: Error #1009: Cannot access a property or method of a null object reference.
	at sisteprosjekt_fla::Symbol1_1/thumbLoaded()

Any suggestions would be greatly apreciated!