iMessage stopped working on Mac Recently, iMessage won't sign in on my MacBook Air (10.8.4). I opened up Messages a couple of days ago, and my iMessage account was signed out. Upon trying to sign back in, I get a message reading:


  The registering device does not have the appropriate credentials.


And login fails. Anyone else have this issue?
Follow the steps listed on this page - http://support.apple.com/kb/TS4476

If that doesn't fix your problem, try checking your Date &amp; Time settings (Settings > Date &amp; Time). Make sure "Set date and time automatically:" is ticked, and that your time zone is correct.