vBulletin Database Error!

Plz ! help me :(
Database error in vBulletin 3.6.8:

Invalid SQL:

UPDATE session
SET lastactivity = 1202064534, location = '/forum/attachment.php?attachmentid=362&d=1199520302', inthread = 1574, incalendar = 0, badlocation = 0, useragent = 'Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 5.1; InfoPath.2; .NET CLR 2.0.50727; .NET CLR 1.1.4322)'
WHERE sessionhash = '2d8cee84397de1bfd97fc9346e570633';

MySQL Error : MySQL server has gone away
Error Number : 2006
Date : Sunday, February 3rd 2008 @ 11:57:07 AM
Script : http://xxx.org/forum/attachment.php?attachmentid=362&d=1199520302
Referrer : http://xxx.org/forum/showthread.php?t=1574
IP Address : 82.99.197.178
Username : navid
Classname : vb_database

We were plagued with the same error
MySQL Error : MySQL server has gone away
Error Number : 2006
for a month long period last year. Get in touch with your host.
It's server related not your vBulletin installation.
In our case the problem arose after a server relocation.