I was running Ubuntu 12.04 and Win7 on the same box, but on seperate disks, and stupidly decided to upgrade my Win7 to Win8. I disconnected my Ubuntu drive (as I don't trust Windows not to mess up GRUB), and everything installed fine. I then reconnected the drives, and had to change the boot sequence in BIOS so that my Ubuntu drive would be first. After a grub update, Windows was showing up as Windows 8 in GRUB, but when I choose it, the blue window logo comes up for a few moments, followed by an error message for a fraction of a second which says error 0x00000050, and then the computer reboots.
I think that the source of the problem is that Windows hibernates when you do shutdown, and when you boot it from GRUB, it fails to "de-hibernate" for some reason. When I tried mounting the Windows partition in Ubuntu, it insisted I do it as read-only, as the disk was hibernated.
I've tried boot-repair and update-grub, but neither worked. I also think they attack a different problem than what I'm having.
Has anyone found a solution to this problem?