JavaScript runtime error

}
   function EnsureCompletionDateNULL() {
     var retval = true;
     var txtbx = document.getElementById('xbIACA__IACA_Completion_Date');
     if (txtbx.value != "") {
       alert("The Completion Date must be removed to continue with the requested action.");
       setTimeout(function(){txtbx.focus().select();},1);
       retval = false;
     }
     return retval;
   }