title: Failed to enter Game Center Sandbox
body: <p>When developing a game center app, I found the sandbox mode is very unpredictable. My game and two devices worked for a while in sandbox mode. After some code are modified (not game center related), recompiled and started debugging, then I get the famous "This game is not recognized by game center" message. </p>
  
  <ul>
  <li>Delete the app</li>
  <li>Sign out Game Center from the Game Center app</li>
  <li>Restart debugging the app</li>
  </ul>
  
  <p>does <em>not</em> help.</p>
  
  <p>Any help is appreciated.</p>