vBulletin Database error emails..

[TBevilacqua]

Guys for a while now we've been recieving alot of emails about errors on pages outside the forums.. it doesn't make much sense, heres an example email:

Database error in vBulletin 3.6.5:

Invalid SQL:

UPDATE session SET lastactivity = 1181161818, inforum = 0, inthread = 0, incalendar = 0, badlocation = 0 WHERE sessionhash = '3451f3d966e5aaa02a5c616364e75023';

MySQL Error : MySQL server has gone away
Error Number : 2006
Date : Wednesday, June 6th 2007 @ 03:53:16 PM
Script : http://www.domain.com/
Referrer :
IP Address : IP ADDRESS HERE
Username : Unregistered
Classname : vB_Database

I've been getting them for a while now, heres my my.cnf:

[mysqld]
safe-show-database
#old_passwords
back_log = 75
skip-innodb
max_connections = 650
key_buffer = 256M
myisam_sort_buffer_size = 64M
join_buffer_size = 1M
read_buffer_size = 1M
sort_buffer_size = 2M
table_cache = 4000
thread_cache_size = 484
wait_timeout = 1000
connect_timeout = 400
tmp_table_size = 256M
max_heap_table_size = 256M
max_allowed_packet = 64M
max_connect_errors = 20
thread_concurrency = 5
read_rnd_buffer_size = 524288
bulk_insert_buffer_size = 8M
query_cache_limit = 5M
query_cache_size = 96M
query_cache_type = 1
query_prealloc_size = 131072
query_alloc_block_size = 65536
default-storage-engine = MyISAM

[mysqld_safe]
nice = -10
open_files_limit = 8192

[mysqldump]
quick
max_allowed_packet = 16M

[myisamchk]
key_buffer = 64M
sort_buffer = 64M
read_buffer = 16M
write_buffer = 16M

[mysqlhotcopy]
interactive-timeout

anything else, please ask!

Thanks.