Take for example the latest OS X 10.11.4 update that was pushed out to Mac users recently. According to several user reports, it seems that after updating to OS X 10.11.4, there are more than a few users who are claiming that they are unable to log into services like iMessage and FaceTime.
So far users have tried all kinds of ways but to no avail. Some even tried fresh installs but that did not seem to fix the problem. According to one user, “Nothing works… I tried two fresh installs before calling Apple and they wanted me to try another – third – fresh install. When I questioned their reasoning they checked and realized there was an issue. I thought this would be fixed within hours. Still no sign of a fix. Really annoying.”
Of course there are some who have had luck with some of the solutions posted, but none of them seemed to offer a guaranteed fix. Either way if you are experiencing these problems, then we suggest you try everything, or if not you’ll have to wait until Apple releases a fix for it.