multi-touch problem in the " Space Shooter to Mobile" tutorial

Hi, i was following this: link text

tutorial and everything works fine except the multi-touch parts. i have two button that are actually two different images in the canvas but when i use one i can't use the other touch button. :(

here is the code:

 using UnityEngine.UI;
 using UnityEngine.EventSystems;
 using System.Collections;
 
 public class SimpleTouchShoot : MonoBehaviour, IPointerDownHandler, IPointerUpHandler
 {
     private bool touched;
     private int pointerID;
     private bool canFire;
     
     void Awake()
     {
         touched = false;
         canFire = false;
     }
     
     public void  OnPointerDown (PointerEventData data)
     {
         if(!touched)
         {
             touched = true;
             pointerID = data.pointerId;
             canFire = true;
         }
         
     }
     
     public void OnPointerUp (PointerEventData data)
     {
         if(data.pointerId == pointerID)
         {
             touched = false;
             canFire = false;
         }
         
     }
 
     public bool CanFire ()
     {
         return canFire;
     }
 }
 

i'm using unity 4.6 by the way.