Error al enviar mensaje privado en el foro

Database error in vBulletin 3.8.2:

Invalid SQL:

                    UPDATE vbulletin_user
                    SET pmtotal = pmtotal + 1, pmunread = pmunread + 1, 
                    pmpopup =
                    CASE
                        WHEN userid IN(16) THEN 2
                    ELSE pmpopup
                    END
                    
                    WHERE userid IN(16);

MySQL Error   : MySQL server has gone away
Error Number  : 2006
Request Date  : Monday, July 13th 2009 @ 01:30:36 PM
Error Date    : Monday, July 13th 2009 @ 01:31:07 PM
Script        : http://miforum.com/private.php?do=insertpm&pmid=
Referrer      : http://miforum.com/private.php?do=newpm&u=16
IP Address    : My Ip
Username      : My User Name
Classname     : vB_Database
MySQL Version :