Trying to upgrade from 8 to 8.1 resulted in a "Next, you'll set up your account' which took forever.
After a Cancel the enter password screen re-appeared but now way to enter it and the sceen freezes.
Eventually the OS rolled-back to 8 and displayed the 0xC1900101 0x40019 error.
Tried this several times with the same result (what else would you expect ;-)
Also ran the
DISM.exe /Online /Cleanup-image /Restorehealth
and tried the upgrade with only the mouse and keuboard attached.
No change.
What DID work is this:
After accepting the license terms the procedure asks for your password.
This time I did not enter it but used the "I'm not ..." choice at the left bottom of the screen.
The procedure continues with 'finalizing' and finaly will finish and ask for your password again.
Here I entered it and all was fine..
Not sure if this is 'the tric' or if it only works in my case..
What I also noticed is that at the time the procedure fails (so before you trun off/on your PC to recover form that) the OS seems to be up and running and all services seem to have loaded. I know because I could connect to the shares and most of all could connect to it using VNC. This is also why I was able to make screenshots :-)
Well good luck to you all, you might/will need it.
I had this problem too and can say that the above quoted advice worked for me. You have to not put in your password and instead select the link at the bottom that says, "I am not [user name]".