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If you receive error "0x800F0A12" when trying to install Service Pack 1 (SP1) for Windows 7 or Windows Server 2008 R2, it means the installer can’t access the system partition of your computer’s hard disk to update files.
Usually, this partition is accessible to Windows (although you can't browse it in Windows Explorer). However, in some situations, access to the system partition might be blocked after Windows has started. For example:
• The system partition isn’t automatically mounted, or made accessible to Windows, during startup.
• A hard disk containing the system partition was removed prior to beginning SP1 installation.
• Windows is running on a storage area network (SAN), and access to the system partition has been disabled.
• A disk management tool from another software manufacturer was used to copy (or clone) the disk or partition on which you’re trying to install SP1.
System partition isn’t automatically mounted
If the system partition isn't being mounted during startup, you can use mountvol in Command Prompt to re-enable automatic mounting of all volumes.
Note
Before proceeding, contact your system administrator to understand why access to the system partition was disabled.
1. Click the Start button , and in the search box, type command prompt.
2. In the list of results, right-click Command Prompt, and then click Run as administrator. If you're prompted for an administrator password or confirmation, type the password or provide confirmation.
3. Type mountvol /E and press Enter.
4. Restart your computer, and then try installing SP1 again.
Hard disk containing the system partition was removed
In some advanced disk management or server configurations, you can remove hard disks from a computer without shutting down Windows. This is informally known as hot‑swapping disks or drives.
If a hard disk containing the system partition was swapped out, return the missing disk to the computer and try installing SP1 again.
Access to the system partition isn’t available on a storage area network (SAN)
A SAN connects multiple servers and storage devices on a single network. If you are running Windows from a SAN , contact your system administrator for more information. Or, go to the SAN manufacturer’s support website for information on how to make the system partition accessible.
Partition created using a program from another software manufacturer
If a disk management tool from another software manufacturer was used to copy (sometimes called clone) disks or partitions on your computer, the SP1 installer might not be able to identify the correct system files.
1. Turn off your computer and physically disconnect any external disks or drives that aren’t required for starting Windows.
2. Turn on your computer, and then try installing SP1 again.