make sure on line 1498 of /admin/forum.php looks like
PHP Code:
$DB_site->query("UPDATE forum SET replycount='$numberposts',threadcount='$numberthreads',lastpost='$lastpost',lastposter='".addslashes(htmlspecialchars($lastposter))."',lasttitle='".addslashes(htmlspecialchars($lasttitle))."' WHERE forumid='$forumid'");
I'm sure at this point you have an INSERT query where it should be the update one above.