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

3.  Restart

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:

• Ensure that the System Reserved partition is marked active (you can do this in Disk Management or DISKPART)
• If you dont have a 100MB System Reserved Partition, make sure the drive with your Windows installation is active
• Make sure that the Windows installation is the only active volume on your installation
• If you have a 100MB System Reserved partition and it is marked active, give the partition a drive letter and reattempt the service pack installation
• If you have SnapDrive from NetApp installed, it may need to be removed for the installation to work properly (source: http://communities.netapp.com/thread/13704)
• Your BCD file could be corrupted, this can be checked by running BCDEDIT at an elevated command prompt to see if it returns normal values to you.  If it does not you'll need to rebuild it.
  • Rebuild the BCD store on your system by booting into WinRE and run the command: bootrec /rebuildbcd to rebuild the file
• Lastly, disconnect any external devices, particularly storage devices such as EBooks and thumb drives

Let me know your results.

--Joseph