There can be unexpected issues when working with Apple's Game Center tech. Sometimes when your'e testing a new feature in your game you just want to skip the login and get to the game. Unfortunately there is some lockout logic in Game Center that'll cause more frustration. If you cancel the authentication dialog 3 times, it'll make your game permanently locked out of Game Center in the sandbox account.
While working on Artwork Evolution's upcoming game, Bomb Dodge, I ran into this issue, and it took hours to find a fix. Apple's Game Center documentation does not provide information on it. The good news is that the issue has a workaround if you dig far enough on the Apple Developer Forums or Stack Overflow.
Below is a summary of how to fix the issue as well as replicate it on both the iOS Simulator, iPhone, iPod Touch, or iPad devices.
iOS Simulator: Game Center App to the Rescue
When not logged into a Game Center account, starting the iPhone game will prompt you to authenticate and sign in. If you press "cancel" it will allow you to play the game without authenticating. However, if you repeat this process 3 times (not just in a row), after the third cancel, it will not prompt you to authenticate again. You are essentially "locked out" of Game Center.
If this happens in the iOS simulator, you can remedy it by simply logging into Game Center via the standalone Game Center app. This is also works on an iOS device when locked out of a regular, non-sandbox Game Center account. After logging in through the Game Center app your number of "Cancel"s replenishes to 3 like when we started.
iOS 7.0 Device: Reset All Your iPhone Settings
When using a Game Center sandbox account on an iOS 7.0 device, getting locked out is much more problematic. If you cancel the the authentication 3 times in a row (Note: on the device it must be 3 sequential cancels), logging in via the Game Center app will log you into a regular, non-sandbox account, not the developer sandbox account. Now you can't login to the sandbox version of Game Center and are unable to authenticate.
The only way to get back into Game Center for the sandbox account is to clear your device's settings by going to:
Settings > General > Reset All Settings
Heads Up: It'll reset Wi-Fi network settings, Siri, location settings, etc. On an iPod with Wi-Fi only you'll run into a second issue, no wifi means that you'll never see the authentication prompt for Game Center when you open your game. Make sure you re-connect to Wi-Fi and then open up your game.
Always authenticate with Game Center and don't make that mistake again!