Problem with AS3

Question

Hello, I'm still learning Flash and Action Script 3, however
i decided to try and create a game for a class. I have run into a
problem, which I'm not sure how to fix. When I navigate to the
second frame of the movie and use the buttons I recieve "TypeError:
Error #1009: Cannot access a property or method of a null object
reference.
at Untitled_fla::MainTimeline/team1_select()"
The file is set up as 3 layers, the first is a single key
frame extending the length of the document with only action script.
The second layer contains a single key frame extending the length
of the document, this layer has the navigation buttons, and the
score buttons. The third layer contains a key frame on every frame,
there are duplicated buttons on each frame (win and fail). How
would i fix this? Any help is appreciated, Thanks
The script is fairly simple, as follows
"stop();
prev_btn.addEventListener(MouseEvent.CLICK, prev_frame);
function prev_frame(evt:MouseEvent):void
prevFrame();
next_btn.addEventListener(MouseEvent.CLICK, next_frame);
function next_frame(evt:MouseEvent):void
nextFrame();
team1_btn.addEventListener(MouseEvent.CLICK, team1_select);
function team1_select(evt:MouseEvent):void
team1_light.gotoAndStop(2);
win_btn.addEventListener(MouseEvent.CLICK, team1_increase);
fail_btn.addEventListener(MouseEvent.CLICK, team1_decrease);
function team1_increase(evt:MouseEvent):void
team1_score.nextFrame();
win_btn.removeEventListener(MouseEvent.CLICK,
team1_increase);
fail_btn.removeEventListener(MouseEvent.CLICK,
team1_decrease);
team1_light.gotoAndStop(1);
function team1_decrease(evt:MouseEvent):void
team1_score.prevFrame();
win_btn.removeEventListener(MouseEvent.CLICK,
team1_increase);
fail_btn.removeEventListener(MouseEvent.CLICK,
team1_decrease);
team1_light.gotoAndStop(1);
team2_btn.addEventListener(MouseEvent.CLICK, team2_select);
function team2_select(evt:MouseEvent):void
team2_light.gotoAndStop(2);
win_btn.addEventListener(MouseEvent.CLICK, team2_increase);
fail_btn.addEventListener(MouseEvent.CLICK, team2_decrease);
function team2_increase(evt:MouseEvent):void
team2_score.nextFrame();
win_btn.removeEventListener(MouseEvent.CLICK,
team2_increase);
fail_btn.removeEventListener(MouseEvent.CLICK,
team2_decrease);
team2_light.gotoAndStop(1);
function team2_decrease(evt:MouseEvent):void
team2_score.prevFrame();
win_btn.removeEventListener(MouseEvent.CLICK,
team2_increase);
fail_btn.removeEventListener(MouseEvent.CLICK,
team2_decrease);
team2_light.gotoAndStop(1);
}"

Answer 1

Thanks for the response. I figured out what was causing the
error, for the layer with the duplicated key frames, the original
has the buttons win_btn and loose_btn. for some reason loose wasn't
working so i replaced it with fail, but forgot to update the other
key frames. doing so fixed the issue.