Warning 1090?

1

I’m having the following warning, I’m not really sure if it has any bad effect on my animations or if it matters but it would be really nice if I could fix it somehow:
[COLOR=DarkOrange]
[COLOR=Red]Warning: 1090: Migration issue: The onEnterFrame is not triggered automatically by Flash Player at run time in ActionScript 3.0. You must first register this handler for the event using addEventListener ( ‘enterFrame’, callback_handler).[/COLOR][/COLOR]

Could someone explain why am I getting that warning ?

If this helps, I’m just playing around in AS 3.0, here’s the code ( a class ):

package {
    
    import flash.display.Sprite;
    import flash.events.Event;
    
    public class FirstAnimation extends Sprite {
        private var ball:Sprite;
        
        public function FirstAnimation() {
            init();
        }
        private function init():void {
            ball = new Sprite;
            addChild(ball);
            ball.graphics.beginFill(0xFF0000);
            ball.graphics.drawCircle(0, 0, 40);
            ball.graphics.endFill();
            ball.x = 20;
            ball.y = stage.stageHeight / 2;
            ball.addEventListener(Event.ENTER_FRAME, onEnterFrame);
        }
        private function onEnterFrame(event:Event):void {
            ball.x++;
        }
    }
}

Thanks.