MySQL server has gone away?!?!

[dlewisr]

I've started receiving these emails over the last couple of days. The first email came after I used the auto back up mod manually, ready for a maintenance check. It was stuck in a loop. Then I noticed that when I ran the 'Rebuild Custom Avatar Thumbnails' on the General Update Tools, there was a note at the top saying 'Processing 439 (jpg). Is that the number of avatars I have or does that mean avatar 439 is corrupt? I ask because I have never noticed that before when I have used these toold.

I'm not sure if these two things are related as I am not at all savvy about these things.

This is the email I receive.

Database error in vBulletin 4.2.1:

Invalid SQL:

INSERT INTO cronlog
(varname, dateline, description, type)
VALUES
('cbu_crontask',
1374391680,
'Backup Completed Successfully',
0);

MySQL Error : MySQL server has gone away
Error Number : 2006
Request Date : Sunday, July 21st 2013 @ 08:28:00 AM
Error Date : Sunday, July 21st 2013 @ 08:56:16 AM
Script : http://**sitename***/cron.php?rand=1374391673
Referrer : http://***sitename***/search.php?searchid=167672
IP Address : 81.151.101.195
Username : Unregistered
Classname : vB_Database
MySQL Version :

The number below '('cbu_crontask', is always different except for the beginning 13743*****. Is my db corrupted and if so, how can I fix it,

Is it that avatar 439? If so how do I find an individual image. The avatar stats ay we don't have any Custom Avatars. I mention this as I've never noticed that before, although it could be that I'm a little more aware because I'm now actually looking for things.

Thanks in advance.