I agree with XenForo that the database error is unexpected. But I find it very hard to help you if XenForo doesn’t say anything about what the error actually is. Can you please check if XenForo has some kind of debug mode or error log you can use to find the actual database error?
In error log, i have five errors. But i dont belive they have anything to do with this issue.
Its also possible to enable debug mode.
The errors are in this pastebin document