We are having the exact same issue going from 5.2 to 5.3. We have one connection server internally and one setup as a security server in the DMZ. We ran the upgrade on the Connection server (internal) first and it completed without an issue but we cannot connect through this connection server anyone and the admin site will not display. There are no errors in the Event Log and we got no errors during the install.
I'd love to know if Cdog was able to overcome this and how. We are trying again tomorrow and plan to get support on the phone.