ActionScript 3.0 :: Start 2 Motion Tween And End With Buttons Shown - Error 1009

I am making a webpage for class and i copied all the code from previous projects that i made that worked fine. I made a menu that once you go over the button it starts a 2 motion tweens that end with buttons appearing. i keep getting the message
TypeError: Error #1009: Cannot access a property or method of a null object reference.

The whole code is this
stop();
back.addEventListener(MouseEvent.MOUSE_OVER,back1);
function back1(event:MouseEvent):void {
gotoAndPlay("one");}
pump_link.addEventListener(MouseEvent.MOUSE_DOWN,pump_btn);
function pump_btn(event:MouseEvent):void {
MovieClip(parent).gotoAndPlay("pumpkin_frame", "pumpkin");}