Sprite alpha animation stop working in Unity 4.5?

Hi, I have a 2d game project which was first built on Unity 4.3.4. I just backed up my project and upgrade unity to 4.5.0 and I found out that all of my game animations that change sprite renderer alpha(fade out animations) stop working. Then I tried unity 4.5.1 and it didn't work either. When I downgrade unity to 4.3.4 back, all the animations worked properly but it has issue on scene loading (Took so much time to load and crash). I use this method to track down the alpha value of sprite renderer:

 public class Tracker:MonoBehaviour
 {
     private SpriteRenderer rend;
 
     string message = "";
 
     void Start()
     {
          rend = (SpriteRenderer)renderer;
     }
 
     void Update()
     {
          message = "Alpha = " + rend.color.a;
     }
 
     void OnGUI()
     {
          GUILayout.Label(message);
     }
 }

However, alpha always = 1(which mean animation not working).

Is there any solution to fix this problem? I appreciate any help and sorry about my English.

Thanks