Button problem

Hey all,
AS3 is doing my head in, it is so much more complex trying to do the most basic stuff.
I have a button with and instance name of “a” so I can’t possibly get the instance name wrong in the script. I’m just trying to make it gotoAndPlay frame 46 when the button is clicked but I’m getting a 1120 error.
Here is my code:


stop();

function playMovie(evt:MouseEvent):void {
gotoAndPlay(46);
}

a.addEventListener(MouseEvent.CLICK, playMovie);

have I done something wrong?

Cheers.