Database error?

Database error in vBulletin 3.6.4:

Invalid SQL:

(SELECT permissions, FIND_IN_SET(forumid, '6,3,-1') AS pos, forumid
FROM VB_moderator
WHERE userid = 5 AND forumid IN (6,3,-1)
ORDER BY pos ASC
LIMIT 1)
UNION
(SELECT permissions, 0, forumid
FROM VB_moderator
WHERE userid = 5 AND forumid = -1
);

MySQL Error : MySQL server has gone away
Error Number : 2006
Date : Sunday, March 9th 2008 @ 10:28:08 PM
Script : http://www.******.com/newthread.php?do=postthread&f=6
Referrer : http://www.*****.com/newthread.php?do=newthread&f=6
IP Address : ip numarası
Username : üye nicki
Classname : vB_Database