// see http://kpumuk.info/asp-net/using-panel-defaultbutton-property-with-linkbutton-control-in-asp-net/
function clickButton(e, buttonid){ 
  if (e.keyCode == 13){ 
    var b = document.getElementById(buttonid); 
    if (b) {
      if (typeof(b.click) == 'undefined') {
        b.click = function() { 
          var result = true;
          if (b.onclick) result = b.onclick();
          if (typeof(result) == 'undefined' || result) {
            eval(b.getAttribute('href'));
          }
        }
      }

      if (typeof(b.click) != "undefined") {
        b.click();
        e.cancelBubble = true;
        if (e.stopPropagation) e.stopPropagation();
        return false;
      }
    }
  }
  return true;
}