AS3 / TweenLite - How to return an array element as a variable in TweenLite?

The code is below. When Tweenlite is called it treats "tileList[count1]" as a string instead of a variable name. However the trace seems to return what I would expect (tile1, tile2, tile3...). If I remove "tileList[count1]" from the tween and replace it with a direct call to the MovieClip (tile1, tile2, etc) the code works perfectly...

public class wtpMain extends MovieClip {

    public var tileList:Array = new Array(tile1,tile2,tile3,tile4,tile5,tile6,tile7,tile8,tile9,tile10,tile11,tile12,tile13,tile14,tile15    ,tile16); 
    public var count1:int = 0;


    public function wtpMain() {
        nextButton.buttonMode = true;
        nextDis.mouseEnabled=false; 

        nextButton.addEventListener(MouseEvent.CLICK, nextButtonClickh);

        tileList.sort(randomSort);

    }

    public function nextButtonClickh(event:MouseEvent):void {
        nextButtonClick();
    }

    public function nextButtonClick():void{


        TweenLite.to(tileList[count1], 5, {y:700, alpha:0});
        trace(tileList[count1]);
        count1++;

    }

    public function randomSort(objA:Object, objB:Object):int{
        return Math.round(Math.random() * 2) - 1;
    }
}

}

Thanks!

---added---

Things I've tried:

• Using a vector instead of an array.
• Setting tileList[count1] to a variable and then calling that variable.
• Removing the randomSort.
• Removing count1 and calling the array element directly (ie, tileList[5]).