Asp – Disabling an ASP validation on an event click before it posts back and performs the validation

The asp.net validators do not provide this kind of functionality to conditionally disable the controls. You will need to write your own validator (pretty tough, or see Peter Blum). Better handle it in blur event handler for the textbox.

 <script type="text/javascript">
   $(document).ready(function(){
      $("#<%=yourTextbox.ClientID%>").blur(function(){
         $("#<%=yourDropDown.ClientID%>").attr("disabled","disabled");
         ValidateInputs();//You will validate inputs in this function
      });
   });
 </script>

 <script type="text/javascript">
  function ValidateInputs(){
     //.....Validations......
     if(validattions okay){ 
        $("#<%=yourDropDown.ClientID%>").attr("disabled","");
      }
  }
 </script>

PS:- I'm supposing you are using jQuery, if not please get some time and visit jQuery.com and give it a try.

Change OnClientClick from return isValidTracker() to if (!isValidTracker()) return false;