Set Child Index For The Love Of Cheese!

I have the view class which adds a movieclip asteroidMap from inside a function. asteroidMap contains some Movieclips called priceFlags
I listen for mouseOver and mouseOut and then tweenLite the scale of the target.
I am having trouble with bringing the target(the target priceFlag in asteroidMap) to the front of the display list. I’m getting:

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

Heres ma code(the problem line is in red):

    public function spaceForMap(e:KeyboardEvent):void        {
            
             if (e.keyCode == 32)
                {
                    var shipIconX:Number;
                    var shipIconY:Number;
                    var shipIconXOffset:Number = -80;
                    var shipIconYOffset:Number = 30;
                    
                    shipIconX = (playScreen.rocks.x*-.1182)+25;
                    shipIconY = (playScreen.rocks.y*-.1173)+252;
                    switch(mapOut)
                    {
                        case("false"):
                    
                    
                        asteroidMap = new AsteroidMap((shipIconX), (shipIconY));
                        addChild(asteroidMap);
                    for (var pFA:Number = 0; pFA < asteroidMap.priceFlagsArray.length; pFA++ )
                    {
                        trace("v5501 in for loop for priceFlagsArray");
                        var currentName:String=asteroidMap.priceFlagsArray[pFA].name
                        asteroidMap[currentName+ "PriceFlagOreTextField"].text = _model[currentName+"OreTypeValue"];
                    
                        asteroidMap[currentName+"PriceFlagCargoTextField"].text = _model[currentName+"PaysForCargo"];
                        asteroidMap[currentName].addEventListener(MouseEvent.MOUSE_OVER, priceFlagMouseOver);
                        asteroidMap[currentName].addEventListener(MouseEvent.MOUSE_OUT, priceFlagMouseOut);
                    }
                        
                        
                        updateMode = false;
                        mapOut = "true";
                        break;
                        
                        case("true"):
                        
                                removeChild(asteroidMap);
                                updateMode = true;
                                mapOut = "false";
                            
                    
                        break;
                    }
                        
                    
                }
        }
        
        private function priceFlagMouseOut(e:MouseEvent):void 
        {
            
            TweenLite.to(e.currentTarget, .5, {  scaleX:.2, scaleY:.2 } );
        
        }
        
        private function priceFlagMouseOver(e:MouseEvent):void 
        {
            [COLOR=#ff0000]asteroidMap.setChildIndex(e.target as MovieClip,asteroidMap.numChildren - 1)[/COLOR];
            TweenLite.to( e.currentTarget, .5, {scaleX:2, scaleY:2});
        }