I am experiencing the same problem and thought I would share some new findings. Not a fix per say but maybe it will be helpful in finding a solution.
On a different forum one person reported that he was able to fix the issue by doing a "refresh" on his PC before attempting the upgrade: (http://www.eightforums.com/installation-setup/33447-windows-8-1-update-success-ramdisk-error.html)
I tried the same method but ran into the "Unable to create ramdisk ..." error when I tried to refresh my PC. The difference this time was that I did not have the option to restore to windows 8 since I wasn't performing an upgrade (only a refresh). I was able to get back to windows 8 by doing a hard reset on my computer.
Anyway, I wonder if this is something that is broken in windows 8 for everyone that is experiencing these upgrade problems. If it is, then perhaps it is not the upgrade but some of other software component in windows 8 that is causing the issue.