How do you make the animation restart?

programming flash
1

I want to make a button (text saying “back to menu”) make it so that when you click it, it restarts the animation. I tried but it gives me this error:

TypeError: Error #1009: Cannot access a property or method of a null object reference.
at navysealstest_fla::MainTimeline/frame1()

This is the code I used to get that error:

menu_mc.menu_btn.addEventListener(MouseEvent.CLICK, launchAnimationAgain);
function launchAnimationAgain(event:MouseEvent):void {
	MovieClip(root).gotoAndPlay(1);
}

What’s wrong? Thank you.