Register page Ajax Check user name duplicate, how to resolve

Register page Ajax Check user name repeat
Register page Ajax Check user name repeat

IE now 60 line error: ' null ' is empty or not an object

On the code:

HTML Code

          
  
  
  
 
   
   
 
    
 
     
Add new users
 
    
 
    
 
     
User name:
 
     
*
 
    
 
    
 
     
Password:
 
     
 *
 
    
 
    
 
     
Repeat Password:
 
     
 *
 
    
 
    
 
     
 
    
 
   

  
  

This is the chkuser.php page code:

PHP Code

------Solution--------------------

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