I used the solution but there it prevents another event occuring on button click?

without this script below the page works fine but with it - another event does not work

    <script type="text/javascript">
          function pageLoad(sender, e) {
              $find("FilteredTextBoxExtender1").add_filtered(function () {
                  $get("error").innerHTML = "Email, links and numbers not permitted";
              });
          }
        </script>