IOS 7 doesn't let me switch game center account...

I try to log in with a second Apple ID for the game center so that someone else in the family can play games using their own scores. When I log out and try to log back in with the second account a screen comes on which looks like I am creating a new Apple ID. I have to agree to terms, create a nickname and then it tells me the email address is already in use by another apple ID!!?? And then it says 'internal server error, try again in a few minutes'!

I can however log in with my first Apple ID.

It looks like a serious bug in the game center app or am I doing something wrong.

Is anyone having similar issues or a solution for this?