Looking at this a little closer. You may have missed a note on upgrading.
From the upgrade documentation.
Upload all files and directories from the unzipped UBB™ directory to the UBB™ installation directory, except for the includes, styles, and cache_builders/custom directories. You will want to upload all of the .php files within the cache_builders directory, just make sure not to upload the custom directory or files within it.
If this is the case. If you have a backup of the site before upgrading.
Upload your backup files to includes,styles and cache_builders/custom directories only.
