When testing,... I get on my device on my iPhone: This game is not recognized by game center! Is it a mistake on me?

If the app worked on the simulator, then it should work on you phone once the app is published. If I remember right, you can only test the gamecenter on the simulator, and not on your actual device. If you search google for this error, you'll see some threads on stackoverflow and some other sites about this. You can only test it in the "sandbox" mode until the app goes live. If you try to test it on your actual device, the servers at apple try to link up the phone's gamecenter with the live ones, and until the app is published you they don't transfer over the leaderboards and achievements to the live servers. Hope this helped.

You can test Game Center on your device. A few things to check: Is the version the same in Xcode and in ITC. They have to be EXACTLY the same, like 1.63 and 1.63 In ITC, is Game Center Enabled clicked? Final resort. Log out of game center. Delete app and game center from the recently used list. Recompile app, run it, and it should sign you into the ***sandbox***. If it doesn't say that, go back and check the first 2 things.

@jbrzensk thanks for the info. Last time I tried to do this it didn't work for me, but maybe it will next time. One thing though. You have to create a couple of sandbox accounts and go through to app. You won't see any of the players on the scoreboard or the scores unless you have at least two posting scores.

I had this very problem with my wifes iPhone earlier today. With hers, I had to close Angry Birds and Scrabble too, which were keeping her GameCenter logged in (or just preventing from going to sandbox, I am not sure which). 2 sandbox accounts needed to show scores. 1 for achievements.