If you are accessing the upgrade via http://ipaddress, but your forum's base URL is actually set to http://yourforum.com, and ipaddress would block an outgoing call to yourforum.com, then it is possible this is what you were facing. Also, if ipaddress is not listed in the forum's POST Referrer Whitelist settings, then the forum might be refusing to process the request at that end. In either case, your firewall would be configured to block itself. If neither one is canonized, ideally ipaddress and yourforum.com would whitelist each other.