ActionScript 3.0 :: Flash Presentation - Motion Tween To Control Object Status?

I made a little flash presentation where a bulb increases in brightness as the mouse goes over it and decreases as the mouse goes out. I set up the object on the stage and created a motion tween equal to 30 frames in which the object starts dull and increases in brightness. To control it, I made this little script:

ActionScript Code:
stop();
addEventListener(Event.ENTER_FRAME, startScan);
mcBulbLit.addEventListener(MouseEvent.MOUSE_UP, startShow);
function startShow(event:MouseEvent):void {
gotoAndPlay(31);
} function startScan(event:Event):void {
[Code] .....
For some reason the bulb only goes back one frame and then stops at that frame.