Ping not work after node create/update

    // Get max creation and modification time
    $res_time = db_fetch_object(db_query('SELECT MAX(n.created) AS created, MAX(n.changed) AS changed FROM {node} n ' . implode(' ', $sql_join) . ' WHERE ' . implode(' AND ', $sql_where), $sql_values));
    if ($row_time) {
      $lastmodified = max($res_time->created, $res_time->changed);
    }
    else {
      $lastmodified = 0;
    }

variable $row_time is always undefined and $lastmodified always = 0. $res_time should be replaced by $res_time