When you do the upgrade, close your forums. After you upgrade check the file permission section in the cp. Sometime you will have to go in and change some file permissions.

I have noticed on some upgrades when going through the installer it may fail at points saying it cannot write to file. Just ftp in, change the file permission and proceed. Files 666 and directories 777

As always, be sure you have a backup of your db and files before you get started just in case! And don't forget

Originally Posted by Gizmo
When running an upgrade be sure to not upload the following directories:
includes/
cache_builders/custom
styles/

Otherwise you'll find yourself with quite a large mess on your hands...