Microsoft rolled out a Cumulative Update for Windows 10 – KB3081424 today. It downloaded and tried to install – got about 30% of the way through, rebooted and then went through a number of reboot cycles to uninstall the changes.
suggested that deleting keys related to orphaned profiles (users no longer exist) from
may fix the problem. As it happened I had an orphaned profile key, deleted it and retried the install of KB3081424.