By any chance does your server use CPanel? We have a theory that the latest version of CPanel is updating MySQL on a daily basis. Unfortunately if your database is being written to when this occurs, then you could get database corruption.
Find out if you are using CPanel and if so, what version it is. Also find out what the update schedule is set to.
http://www.vbulletin.com/forum/showt...605#post438605