email problem (help plzz)

[Osama11]

Database error in vBulletin ****:

Invalid SQL:

UPDATE session
SET lastactivity = 1207355835, location = '/admincp/email.php?do=dosendmail&do=dosendmail', inforum = 0, inthread = 0, incalendar = 0, badlocation = 0, useragent = 'Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.0; SLCC1; .NET CLR 2.0.50727; Media Center PC 5.0; .NET CLR 3.0.04506)'
WHERE sessionhash = '99d3980970270ebbc8a099231c98f592';

MySQL Error : MySQL server has gone away
Error Number : 2006
Date : Friday, April 4th 2008 @ 06:39:49 PM
Script : http://**************/admincp/email.php?do=dosendmail
Referrer : http://************/admincp/email.php?do=start
IP Address : ******************
Username : DON



when i send a email to users its show me this error before click the next button...
any 1 know y
plzz help me