File download in vBulletin does not complete
If you get a “MySQL server has gone away” when using the file download feature in vBulletin, this probably means that your forum’s attachments are stored in the database.
This increases the size of the database which results in slow MySQL queries that eventually lead to the above error message.
To resolve the issue, move your attachments from your database to the file system. You can do this from your vBulletin admin panel > Attachments > Attachment Storage Type.
To move the attachments from the database to the file system, click on Go. This should resolve your problem.