How to Fix Error 0x800F0818 when Installing Service Pack 1 (Windows 7)

Step-by-Step Guide

1. 1

   Step 1: Find and download the System Update Readiness Tool for the version of Windows you are working on.

   The tool can be found on the Microsoft website with a quick Google search.
2. 2

   Step 2: Run the System Update Readiness Tool installer you downloaded.

   "Installing" the tool will also run it for the first time. ,, 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. , As an example:
   Package_for_KB2506014_RTM~31bf3856ad364e35~amd64~~6.1.1.0.mum and Package_for_KB2506014_RTM~31bf3856ad364e35~amd64~~6.1.1.0.cat. , Make a note of the number. ,, Do not run the installer. , Alternatively you can use the Expand
   -f: command line utility. ,,, You should see that the files have been repaired. ,
3. 3

   Step 3: Open Windows Explorer (Start - Computer) and navigate to "%systemroot%\Logs\CBS\" using the address bar.

4. 4

   Step 4: Open CheckSUR.log using Notepad or a similar text editor.

5. 5

   Step 5: If there are unavailable repair files you will see two or more packages.

6. 6

   Step 6: In the file name should be a number proceeded by "KB" (KB2506014 in this example) which is is the update package that is corrupted.

7. 7

   Step 7: Open a browser window and navigate to support.microsoft.com/kb/(number here) for example support.microsoft.com/kb/2506014.

8. 8

   Step 8: Find and download the package for your version of Windows on the resulting page.

9. 9

   Step 9: Use an extraction utility like 7-Zip to extract the CAB files from the MSU installer and then again to extract the contents of the CAB files.

10. 10

    Step 10: In the extracted files locate the .mum and .cat files mentioned in the CheckSUR.log.

11. 11

    Step 11: Copy the .mum and .cat files to "%windir%\Temp\CheckSUR\servicing\Packages"

12. 12

    Step 12: Run the System Update Readiness Tool installer again and check the CheckSUR.log file from steps 3 and 4 when it is finished.

13. 13

    Step 13: Install Service Pack 1 normally.

Detailed Guide

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