Trying to return to menu after video ends

I have a very simple bit of AS3 that I can't get to work. I have 4 FLVPlayBack's on 4 frames, buttons on a menu to go to the frames to play the videos, and I need to return to the menu's frame after the videos end. Here's what I have. The buttons to play the videos work, but the function to return to the menu isn't firing. I'm also getting this error as the program starts. Not sure if this has anything to do with it.

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

iimport fl.video.VideoEvent;
stop();

//button listeners

btn_tour.addEventListener(MouseEvent.CLICK, tourClick);
btn_history.addEventListener(MouseEvent.CLICK, historyClick);
btn_quality.addEventListener(MouseEvent.CLICK, qualityClick);
btn_song.addEventListener(MouseEvent.CLICK, songClick);

//video end listeners

tourVideo.addEventListener(VideoEvent.COMPLETE, backtomenu);
historyVideo.addEventListener(VideoEvent.COMPLETE, backtomenu);
qualityVideo.addEventListener(VideoEvent.COMPLETE, backtomenu);
songVideo.addEventListener(VideoEvent.COMPLETE, backtomenu);

//button functions

function tourClick(event:MouseEvent):void{ gotoAndStop("tour"); };
function historyClick(event:MouseEvent):void{ gotoAndStop("history"); };
function qualityClick(event:MouseEvent):void{ gotoAndStop("quality"); };
function songClick(event:MouseEvent):void{ gotoAndStop("song"); };

//head back to menu function

backtomenu(){
    trace ("Video ended!");
   gotoAndStop("menu");
}

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