Well, turn on your mysql error logs in the UBB so they log to a file:
CP -> Master Settings -> Primary Settings -> Logging Tab
Then you might change "$showerror = 0;" to "$showerror = 1;" in the "libs/mysql.inc.php" file so that errors are shown directly to the browser vs the "only visible to admin's" error being displayed (I'd only do this while testing).
From here, when an error is triggered just write down what's displayed (in any log file, the one for the UBB which should display to the browser with the change to mysql.inc.php, and your server logs) and we can attempt to pinpoint why things won't work.
