This seems to be the issue with game center connect. The little popup controller which shows that you're connected doesn't support landscape or something?

Apparently it's a bug in iOS6, and Apple suggests this workaround:

Game Center
Landscape-only apps that invoke a portrait-only view controller (such as the Game Center login screen) will cause the app to crash.

Apps should provide the delegate method application:supportedIntefaceOrientationsForWindow and ensure that portrait is one of the returned mask values.
When a UIBNavigationController is involved, subclass the UINavigationController and overriding supportedInterfaceOrientations.