While upgrading mine W8 to W8.1, I have encountered an installation error. The download in Windows Store got stuck on 50% with an error 0x80070002. Google didn’t show up any relevant results (well, it was the first day after W8.1 release). Going through the logs c:\$Windows.~BT\ was more or less useless. I focused my mind on any configuration setting, that wasn’t ordinary and there it hit me - I use grub multiboot for my Windows and Debian systems. The solution was on its way. What I tried first (as I didn’t want to remove my Grub bootloader), I just tried to switch the active partition to my C: drive and it worked like a charm. Even after installation, the Grub bootloader is still working OK without any reconfiguration.

Solution

1. Go to lower left corner of your Desktop and right-click on the little metro screen (or just click Windows key + X)
2. Choose Disk Management
3. In the disk management configuration dialog, right-click your windows partition (usually the one with C:)
4. Choose Mark Partition as Active
5. That’s it. No need to reboot. You can switch back to your Windows Store and continue with Windows 8.1 downl