Shootorial #5: ActionScript 3

I get the output error:
ArgumentError: Error #2025: The supplied DisplayObject must be a child of the caller.
at flash.display::DisplayObjectContainer/removeChild()
at EnemyShip/kill()
at EnemyShip/enterFrame()
when the enemyships are out of range (when they are supposed to be removed from the stage). How do i fix this?

function enterFrame(e:Event){
this.x += speed;
if (this.x > 600){
removeEventListener(Event.ENTER_FRAME, enterFrame);
stage.removeChild(this);
return;
}

for (var i in EnemyShip.list){
if (this.hitTestObject(EnemyShip.list[i])){
removeEventListener(Event.ENTER_FRAME, enterFrame);
stage.removeChild(this);
EnemyShip.list[i].kill();
break;
}

if we say removeEventListener() why must we say return? Surely once the event listener is removed the entire function becomes inoperative? Could someone please explain what happens once an event listener is remove. I thought it automatically exists the function.

I'm getting an Error #2007: Parameter hitTestObject must be non-null... but my code is exact the same as the examples... someone can help?

To get the explosion movie clip, you need to extract the Untitled-1.fla, open it, copy the explosion movie clip from the library, then paste it onto the stage of your game.

i'm having the same problem as chaxnoir
if this is months after i will ask on moly's profile...