"Couldn't update to Windows 8.1 - 0xC1900101 - 0x40017"

I think you may have misunderstood what I said.

I restored a full sector by sector image of  Windows 8.0 made with Acronis True Image 2013 over the fresh install of the Windows 8.1 to restore my computer to the state it was in before I tried to upgrade my windows 8.0 install.  I am currently running 8.0 because I did not want to go thru the hassle of reinstalling all my apps and re-initializing my steam install. I have steam on a separate drive.

However what you are proposing might work using the windows backup function, not sure how that would turn out, ie how you could just restore your apps and files without affecting the registry or the dll's  or some othe OS setting upgraded or installed during the upgrade process???

Might be worth a shot but I would make certain you have a iron clad Image before attempting.

Good luck

Ah... OK.  Yeah... I'm making a backup and am going to try a refresh to start from scratch, then update - if all goes well, I'll evaluate the hassle from there.

The thing is that I have 180 newer games installed on that PC - each one went through an install process that may or may not have modified registry settings.  If it fails catastrophically, Steam would require re-download of each one.  4Gb (rough estimate per game?) x 180 = Comcast knocking on my door.

Is there any chance Microsoft could acknowledge this problem? I have tried this now 7 times. Updated Nvidia drivers, Updated ALL drivers that are available on ASUS site. Updated BIOS. Tried clean boot, tried everything. But the update keeps failing and a new pc that does not have anything strang. Even disabled all the non essential devices in the BIOS. 

Please help.

I'm not sure if someone from MS is watching this thread but I have tried to install 8.1 in 4 different machines, and I'd like to share my experience. 

PC-1 (custom-build): failed to update to 8.1. four times. I followed all instructions here but with no effect.

PC-2 (xps14): install smoothly - no problem at all!

PC-3 and PC-4 (custom-build): They updated to 8.1 but with problems. In both PCs most of the user accounts applications in tile interface where destroyed (I mean MS apps like Mail for example). The skydrive of user accounts was pointing in PC-3 to the skydrive folder of the admin account. In both PCs I had to delete user accounts and rebuild them from scratch. I also had to reinstall nVidia drivers cz they didn't load correctly and were slowing down both PCs. Now they all work fine.

So, is this mess supposed to happen? I mean, I saw 4 different "behaviours" in four different PCs!! Is there anyone from MS to give some real answers please??

I've updated all possible drivers for 8.1 and also updated my graphic drivers for ATI.  Still no go.