Null object reference starling

Question

This function is called within a for loop to create 4 buttons ... select the right frame and display it.
Problem is I get a null object reference in addChild... line.
I'm using starling and I don't know how to get rid of this error. Can you help ?
private function newButton(i:int):void
                              var newBtn:_menuButton = new _menuButton();
                              newBtn.gotoAndStop(i + 1);
                              menuGroup[i] = newBtn;
                              addChild(newBtn as DisplayObject); //starling.display.DisplayObject
                              newBtn.addEventListener(TouchEvent.TOUCH, onTouch, false, 0, true);
Also the code on Starling :
        public function addChild(child:DisplayObject):void
            addChildAt(child, numChildren);
        /** Adds a child to the container at a certain index. */
        public function addChildAt(child:DisplayObject, index:int):void
            if (index >= 0 && index <= numChildren)
                child.removeFromParent(); //I get error in this line primarly.
                mChildren.splice(index, 0, child);
                child.setParent(this);               
                child.dispatchEvent(new Event(Event.ADDED, true));
                if (stage) child.dispatchEventOnChildren(new Event(Event.ADDED_TO_STAGE));
            else
                throw new RangeError("Invalid child index");

Answer 1

Also _menuButton is a flash MovieClip ... I am thinking you can't unite flash and starling this way ...maybe have to implement it using starling MovieClip.