All,
i tried all the suggestions here and nothing worked until I tried something different today. I have 2 Apple IDs, due to being a long time Apple user and also subscribing to MobileMe, prior to icloud. What I decided to do today was use my 2nd Apple ID in Gamecenter instead of my primary one, attached to my main email. I logged in with it, and then created a new Gamecenter account. After completing account setup, I went back to my GC preferences inside Settings, then logged out, and logged back in with my primary, original email. Voila! Gamecenter returned back to normal 100% with all my old games loading properly, as they have bewn doing on my iPad.
if you've tried everything else, and nothing has worked, try this. Hopefully it will fix you issue like it did mine.