Service Pack installation failed with error code 0x800f0818.

If on (fresh installed) Windows Server 2008 R2 you are not able to install SP1 with error code 0x800f0818 in System's Event Viewer (Event ID 8), check this log file: "C:\Windows\Logs\CBS\CheckSUR.log" (after installing KB947821).

Then, maybe you'll want try following steps:

1. Download this x64 KB from Microsoft (Security Update for Microsoft .NET Framework 3.5.1 on Windows 7 and Windows Server 2008 R2):

http://www.microsoft.com/download/en/details.aspx?displaylang=en&id=26289

2. Expand the msu package.

Example:
expand C:\sourceDir\Windows6.1-KB2518867-x64.msu /f:* c:\tempDir

3. Expand the cab file.

Example:
expand C:\tempDir\Windows6.1-KB2518867-x64.cab /f:* c:\targetDir

4. Change Ownership of "C:\Windows\servicing\packages" folder to your account and give for your account full control privilege (you will need it for last step).

5. Replace this files***:
   C:\Windows\servicing\packages\Package_for_KB2518867_RTM~31bf3856ad364e35~amd64~~6.1.1.0.mum
   C:\Windows\servicing\packages\Package_for_KB2518867_RTM~31bf3856ad364e35~amd64~~6.1.1.0.cat

   with the same name files from "c:\targetDir"



*** files for step 5 may be different according to errors in CheckSUR.log file.