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

I have been having the same issue. I recently updated my custom built computer, reformatted the raids, and installed windows 8 clean. after running windows update and checking for new drivers the system seems to be happy. however, when i run the windows 8.1 update i get the same error. After trying everything above several times the update still fails. At this point i decided to get Microsoft involved and contacted one of their techs. I gave him remote access and after running a couple scans he tells me the update is failing due to some kind of leftover corruption from the old windows 7 install and he knows what the issue is and can fix it but that type of support is only for their "premium users" which will cost me $100. he can not even point me at a specific problem or tell me how to fix it on my own without me paying for it. so i imagine many of the people who are still having issues after following all the steps listed in this thread are actually having the same issue as me. so just take comfort in the fact that Microsoft knows what the issue is and they will be glad to tell you as long as you pay them more money

I have found Revo Uninstaller finds left over and hidden files, easy to use too.

To LeoGeth.  I do not believe Microsoft Support knows how to fix the problem, even for a fee.  Myself and others have had a bad experience with them trying to fix the problem.  In many cases, they take over your machine in an attempt to do good, but end up leaving your computer in a sorry state.  Its very risky to let them try to resolve this problem.

Not to mention it's a problem with their software update and they have some nerve trying to charge you to fix it.

Thats what i was thinking as well. It really blew me away that they wanted to charge me to fix a corruption issue that spawned from from their software in the first place.

i've heard that the upcoming 8.2 is not a full update but rather a cumulative one, that means we still have to go through 8.1 at the first place to be able to update to 8.2, I was hoping that they will provide a whole new 8.2 which includes 8.1 along with the 0x40017 error fixed, now it seems it won't be the case, so basically its likely we are stuck with Windows 8 until Windows 9 comes out but even then who knows what will turn out, the worse part is, from what I see, they seemingly have given it all up and simply ask user to reinstall the whole damn Windows 8 thing in order to upgrade to 8.1 and forth, still I personally can't afford doing such thing.