sparo, perchè non uso questi Tween solitamente, prova ad aggiungere la riga in rosso

import mx.transitions.Tween;
import mx.transitions.easing.*;
var myTween:Object = new Tween(mc, "_alpha", Normal.easeIn, 0, 100, 30, false);
var myTween:Object = new Tween(mc, "_y", Normal.easeIn, 0, 100, 30, false);