After I added Game Center, the app crashes at start up, in simulator with iOS prior to version 4.1. Haven’t check it in real devices yet. (Hard to find one.)
I added ‘-weak-lSystem’ option to the link flags as answers to other questions said, but it didn’t work.
How to walk around this? Or I shouldn’t care about that at all?
Just to close it: weak link the GameKit framework will do. Then the app will not crash on devices with iOS prior to version 4.1.