You were able to run the upgrade script without problems? This error appears only on the forums / not in the AdminCP?
Do you use different subdomains for forum, AdminCP, or wiki?
Do any of your subdomains go through symlinks on your file system?
If you use subdomains and/or use symlinks, then you may need vw_config.php files in some, if not all, of the affected directories. You can find this file in the do_not_upload folder of the ZIP, in one of the "subdomain" sections. For each copy of this file you upload, edit the file to specify the canonical server paths for the forums and VaultWiki. I'm not sure why you would suddenly need these files after upgrading, unless you had them before and removed them / overwrote them by mistake when you were uploading.