Question - Frame Jumping Buttons

I’m quite new to flash and as3, and i have this problem:

*** you can see the code on post no’5***

I have a button (lets say bt1) that has an eventListener on frame 1, with a function gotoAndStop (2);

When i click on it, it goes to frame 2. but! when i go back to frame 1 (with another button that works just fine) i get a NULL REFERENCE ERROR.
** bt1 does not exist in frame 2

I noticed that if i had the button in frame 2 as well, this wouldn’t happan (but i can’t put it there)

What’s wrong?