Action Script Question

            addEventListener(Event.ENTER_FRAME, onEnterFrame);

        }

            private function onEnterFrame(event:Event):void {

                var dx:Number = circle_mc1.x - square_mc.x;

                var dy:Number = circle_mc1.y - square_mc.y;

                var angle:Number = Math.atan2 (dy,dx);

                var xVelocity:Number =Math.cos(angle) * speed;

                var yVelocity:Number =Math.sin(angle) * speed;

                square_mc.x += xVelocity;

                square_mc.y += yVelocity;

                circle_mc.addEventListener(MouseEvent.MOUSE_UP, Stopd)

            }

            private function Stopd(evt.MouseEvent):void

            {

                this.square_mc.stop;

            }

Getting the error code

1084: Syntax error: expecting rightparen before dot.

for the enlarged line.