EDIT: The problem was in the question. I dropped the Tapatalk table and the upgrade completed, and the errors went away. So, um, never mind! ^__^
I just upgraded my forum to RC2, and it was pretty painless. The upgrader choked on what seems to be a leftover tapatalk table, but that was at the 98% mark and everything else worked... I had to close that attempt and reload the forum and it seems to be working fine.
But I'm getting a TON of this one error in the logs:
8: Undefined index: global_character_set
https://<domain>/forum2/index.php?type=rss;action=.xml
/var/www/forum2/Sources/Subs.php (Line 862)
Can anyone suggest a fix? 500 errors in ~15 minutes, and no end in sight.