vbulletin apparently has a lot of issues keeping it's databases straight... I've seen this a few times here, and on other forums using the same thing. This database can't be all that big, so I would normally recommend nightly backups rather than weekly, but I'm sure there are reasons.
On that note, I fix computers and servers as a day-job, and if Bernhard ever needs any additional technical consultation that can't/won't be handled by server-farm staff, all he needs to do is ask. I wouldn't dream of charging to help out a free site I used every day.