/**
  * sets an admin area error message
  * 
  * @param string $message the message to be dislayed
  * @param string $type the type of message: 'updated' (yellow) or 'error' (red)
  */
 public static function set_admin_message($message, $type = 'error')
 {
     if (is_admin()) {
         Participants_Db::$session->set('admin_message', array($message, $type));
         Participants_Db::$admin_message = $message;
         Participants_Db::$admin_message_type = $type;
     }
 }