Windows 7 SP1 upgrade - error 0x800f0a12 and the solution

So, I decided to upgrade my Windows 7 installation to SP1 using Windows update.

It did not work and returned the error 0x800f0a12, which means that the updater can not access the system partition (the 100MB partition that Win 7 creates during installation).

After some trial and a lot of error I thought it might be caused by my dual boot setup.

I have grub installed on a separate hard drive from where I boot Windows 7 – I use this setup the preserve the Windows 7 boot block – my hunch is that grub ignores the system partition altogether and that’s why Windows 7 can not see it.The solution was:

1. Reboot machine.
2. Choose boot menu in bios (ESC, F12, whatever your bios wants). In other words bypass GRUB.
3. Choose the disk where Windows 7 is installed.
4. Restart SP1 upgrade.

Wait one hour.

Done.