Seems like every time I try to upgrade to Windows 8.x something horribly goes wrong. This time I had the upgrade continue all the way to "Applying PC Settings 86%" where it got stuck, and rebooting then had the install roll back with the error message:

Couldn't update to Windows 8.1
Sorry, we couldn't complete the update to Windows 8.1. We've restored your previous version of Windows to this PC.
0xC1900101 - 0x40017

I updated the Intel Chipset drivers, updated and patched all drivers installed in my system as well as applied all Windows updates. No change. I then tried the opposite - tried removing all drivers - no difference. Then I disabled all onboard devices in my system BIOS - no difference.

Last but not least I tried uninstalling the Steelseries driver for my Steelseries keyboard and mouse. And voila... The upgrade completed successfully.