AS3 - removeEventListener help

programming flash
1

I have a very simple clock that I would like to get working.
Basically, when you press the “start” button, it begins counting.
When you press “stop”, it stops and resets to zero.

I don’t understand why my code shows an error.
Could someone help me out?

stop();

var sec:Number = 0;
var min:Number = 1;
var buffer:Number = 30;

buttonStart.addEventListener(MouseEvent.MOUSE_DOWN, startdown, false, 0, true);
function startdown(evt:MouseEvent):void {
addEventListener(Event.ENTER_FRAME, clockcount, false, 0, true);
function clockcount(evt:Event):void {
if (buffer >= 30) {
buffer = 0;
sec++;
} else {
buffer++;
}
if (sec >= 60) {
timer.timeMinutes.text = min++;
sec = 0;
}
timer.timeSeconds.text = sec;
}
}

buttonStop.addEventListener(MouseEvent.MOUSE_DOWN, stopdown, false, 0, true);
function stopdown(evt:MouseEvent):void {
removeEventListener(Event.ENTER_FRAME, clockcount);
}