Take it easy. I wouldn't go so far thinking about a fresh install yet. There are some possibilities that might be the cause of your problems.
First of all it seems that your database update from 04x to 058 didn't run correctly. So there might be some entries in your DB missing, such as the "count_users_posts" values in the FORUMS_TABLE. That alone could be the cause of many problems.
Second I thing there might also be some old files left, which haven't been replaced with new ones. That could also be the cause of many errors you might have.
Put those two togehter and it could explain ALOT of problems.
Third you have a XS version with additional MODs which could also cause problems I can not determine.
I think not everything is lost yet. However in order to confirm that, I'd need full access. That mean FTP, DB (mysqladmin) and ACP
Who set up your board?
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