$req = mysql_query("SELECT * FROM `cms_sessions` WHERE `session_id` = '$session' LIMIT 1");
if (mysql_num_rows($req)) {попробуй заменить на это
$count = mysql_result(mysql_query("SELECT COUNT(*) FROM `cms_sessions` WHERE `session_id` = '".$session."' LIMIT 1"), 0);
if ($count > 0) {