TextBox value not getting updated in Ajax PageMethod OnSuccess function.

[ja3_bhende]

I have used Ajax Page Method to call a server side Method for verifying value in textbox.Here is my Code

Javascript Code :

 function VerifyValue()
   {
       var txtCtrl=  document.getElementById('<%= txtCode.ClientID %>');

       PageMethods.VerifyValue(txtCtrl.value,onComplete,onFailure,txtCtrl);

   }

 // Server side method VerifyValue is returning string and executing properly.    
 //  Getting called perfectly and returns 'N'

     function onComplete(result,txtCtrl)
     {
       if (result == 'Y')
       {
            alert("Vsuccessfully");                   
       }
       else if (result == 'N')          // Control goes here
       {         
           [COLOR="Red"] txtCtrl.value = " ";   // Here is the problem,
                                                // textbox not getting  updated[/COLOR]            
            alert("Invalid value!" );           // alert Message is fired perfectly.

        }
      }   

My problem is txtCtrl value which I am setting in 'else' condtion is not getting updated to " ",it remains unchanged.No error is thrown during execution.Please help me urgently.