[cliff p.]

Thanks for your replies. What I ended up doing probably wasn't the best solution:

1. Deleted all files from server.
2. Re-uploaded VB4 PL2
3. Confirmed config.php configured correctly; re-uploaded PL3


Once I did the above steps, I logged in to the admin cp to confirm the software could still talk with the database, and then browsed the forum in the locations that were not working before. Everything now seems to be working fine. Still not sure what exactly caused it. I'm betting there were some files that may have had some edits from the 3.8.x software that got transferred during the migration for update, and they didn't actually get touched by the upgrade.

Regardless, it's working again so I can start implementing the software modifications

--------------- Added [DATE]1354582552[/DATE] at [TIME]1354582552[/TIME] ---------------

I've found the culprit. VBSEO 3.6 causes the issue. Not sure why but that's the problem.

--------------- Added [DATE]1354584683[/DATE] at [TIME]1354584683[/TIME] ---------------

More specifically:

.htaccess file caused the error.