It looks like I'm going to have to completely reinstall Windows to get the Anniversary update. My laptop has a 450MB WINRE partition (before EFI and C partitions), and the update won't install at...

I don't know what caused the problem to start, nor have I found a solution. But ... I restored an EaseUS backup image, and fortunately I can now create Windows system image again.

I've been running two machines with Windows 10 x64 for a while now. I periodically run a system image backup (on each machine) to an external HDD just as an extra precaution, as I use EaseUS ToDo...