Not sure. Maybe check.
1. Has your device been registered on your apple dev account?
2. Are you logged out of your normal game center account on the device
3. Do you have Sandbox mode enabled on the device under Settings-Game Center
Yeah, that's the weird thing, I've done all that and it works if I dump the zip in the iOS CocoonJS app, but if I try to run through Xcode - no dice :
Guess I'll have to submit without Game Center again