TypeError: Error #1009: Cannot access a property or method of a null object reference

Hello,

I am using this method to create a slider to control frames in a movie clip.

var bounds:Rectangle=new Rectangle(SliderControl_MC.x,SliderControl_MC.y,178,0);
SliderControl_MC.addEventListener(MouseEvent.MOUSE_DOWN,dragScroll);
function dragScroll(e:MouseEvent):void {
SliderControl_MC.startDrag(false,bounds);
}
stage.addEventListener(MouseEvent.MOUSE_UP,dropScroll);
function dropScroll(e:MouseEvent):void {
SliderControl_MC.stopDrag();
}

The slider works well when I’m in the scene that contains the slider. When I go to a scene that does not include the slider, I get the following output error.

TypeError: Error #1009: Cannot access a property or method of a null object reference.

How can I stop the stage.add.EventListener when I navigate to other scenes that don’t include the slider.

This is my first as3 project. The project functions as it should but I don’t know if the output error will cause problems later.

Thank you for your help.