The reason for the update was to force the sessionid system to revert to the standard phpbb session system, rather than the stupid ass Prillian sessionid system.

You see, I was working on putting one of those "type these random fuzzy bent letters/numbers in the box before you can register" things, and it didn't work correctly...so rather than troubleshooting it, I decided to uninstall it and go to sleep. Well, while uninstalling it I realized there was a mod on the forum called Prillian that was causing database errors that were associated with the user tables.

Basically, when you register on the forum, usercp_register.php enters all your information into the huge database system (MySQL) that the forum runs on. Prillian was handling some of the variables for those databases directly associated with sessionid (you know how sometimes at the end of a URL you see "sid=f2e351fa3fcab3412"? That's the sessionid.) It, along with the cookie system keeps you logged in. When I replaced the usercp_register.php file with a non-modded one, anyone who registered wasn't satisfying the Prillian tables by inserting the different information into them. When I replaced it with the Prillian modded file, there was a bunch of stale cookie data sitting in one of the tables that refused to drop.

So I said "F*CK it," backed up the entire forum filestructure, dropped the 2.0.20 filestructure over here, added the SQL update script, ran it, and with a few minor .tpl changes, we're back up and running just fine.