Since upgrade to Mountain Lion I am unable to sign into Apple applications. They were working flawlessly with SL and Lion. Applications have the following errors. iCloud Unable to sign in because of a problem communicating with iCloud. Try signing again. App Store An unknown error has occurred. FaceTime The server encountered an error processing registration. Please try again later. Messages The server encountered an error processing registration. Please try again later. I have tried almost everything I could find in the forum. But feel free to repost in this thread any fixes you may have. I will respond as I try them.