Вот, проверь
mysql_query("UPDATE `users` SET
`postforum` = '" . ($datauser['postforum'] + 1) . "',
`gold` = '".($datauser['gold'] + 5)."',
`lastpost` = '" . time() . "'
WHERE `id` = '$user_id' "); Вот, проверь
mysql_query("UPDATE `users` SET
`postforum` = '" . ($datauser['postforum'] + 1) . "',
`gold` = '".($datauser['gold'] + 5)."',
`lastpost` = '" . time() . "'
WHERE `id` = '$user_id' ");