setChildIndex() and e.target

Hello,

I have a movieclip with the instance name of **container **and in that other movieclips that are partly on each other.
What I’m trying to do, is that if the mouse goes on a movieclip inside the container it comes front (depth goes to 0).

My code:

container.addEventListener(MouseEvent.MOUSE_OVER, mouseOn);

function mouseOn(e:MouseEvent):void{
this.setChildIndex(e.target, this.numChildren-1);
}

when I trace the e.target it gets me the correct instance names of these objects but when I run it I get an error.

1118: Implicit coercion of a value with static type Object to a possibly unrelated type flash.display:DisplayObject.

Could anyone help me please?