You might encounter an issue during the installation of SP1 for Win7/R2 where the installer exits with: 0x800f0a12
This is due to the automount policy for your machine being set to disable. We block the service pack installation in these cases because we need to be able to write information to the BCD store during install and with automount turned off, we are not able to. To resolve this, re-enable automount and then install the service pack. Quick steps to do this in case you forgot are:
1. Run DISKPART
2. automount enable
4. Install SP1
An additional link: http://windows.microsoft.com/en-US/windows7/windows-7-windows-server-2008-r2-service-pack-1-sp1-installation-error-0x800F0A12
If your problem is not automount policy then you might have one of the other scenarios which can cause this error to occur (such as a third party boot loader). Here are some other steps to try:
Let me know your results.