var ModalProgress = 'ctl00_ModalPopupExtender1';
      Sys.WebForms.PageRequestManager.getInstance().add_beginRequest(beginReq);

      Sys.WebForms.PageRequestManager.getInstance().add_endRequest(endReq);

      function beginReq(sender, args) {
          
          // shows the Popup 

          $find(ModalProgress).show();

      }



      function endReq(sender, args) {

          //  shows the Popup 

          $find(ModalProgress).hide();

      }