How to Fix Error 0x800F0818 when Installing Service Pack 1 (Windows 2008 R2)

Reference:
http://www.wikihow.com/Fix-Error-0x800F0818-when-Installing-Service-Pack-1-(Windows-7)

1. search and download "System Update Readiness Tool" on http://www.microsoft.com/en-us/download/default.aspx
2. install "System Update Readiness Tool"
3. check log file c:\windows\logs\cbs\CheckSUR.log
• If you see a number of fixed files at the top of the log: try to install Service Pack 1 again.
• If you see anything under "Unavailable repair files": keep reading.
4. fix the unavailable repair files, ex: Package_for_KB2506014_RTM~31bf3856ad364e35~amd64~~6.1.1.0.cat.
• open http://support.microsoft.com/kb/2506014
• Find and download the package for your version of Windows. Do not run the installer.
• extract the cab file by 7-zip
• copy the extracted file Package_for_KB2506014_RTM~31bf3856ad364e35~amd64~~6.1.1.0.cat to c:\windows\Temp\CheckSUR\servicing\Packages
5. Run the System Update Readiness Tool installer again and check the CheckSUR.log file from steps 3 and 4 when it is finished. You should see that the files have been repaired.
6. Install Service Pack 1 normally.