I’m on a perfectly healthy mid-2013 AirBook, maxed-out, but otherwise plain vanilla (no haxies or such), which I had updated to 10.11 without any problems. (I’m backed up with a bootable clone plus Time Capsule, so my data’s safe.) I couldn’t update to .1, and now, not to .2, either. Since the problem with .1, I’ve done - repeatedly - everything I could think of to fix it (repaired with DW and TTP, tried everything relevant listed here <http://macs.about.com/od/MacTroubleshootingTips/tp/Top-10-Troubleshooting-Tips-F or-Mac-Startup-Problems.htm>).
Since I don’t want to stop working on my Mac while updating, I’m attempting to update the clone, on an external disk via Firewire 800, using the 10.11.2 combo update which I have on a flash drive (I had tried .1 directly on my AirBook). The result: progress bar fills - creeps more and more slowly as it nears the end - to what looks like 100%, and stays there. Nothing more happens, even waiting overnight.
Curiously, my wife's slightly newer AirBook had no problem at all with .1 - I haven't tried .2 yet.
I’ve never had a problem like this since I began using Apples, in 1984. It’s surely a software problem, not hardware or disk space. I don’t know how many users worldwide are having this problem, but judging by what I read, it’s probably only a small percentage, not large enough for Apple to attend to it. Still, I don’t know what those of us who are affected can do. Apparently, Genius Bar people can’t help, either. I’m really dismayed and angry. Will I be stuck with 10.11 forever?