2026-02 Security Update (KB5077181) (26200.7840) error code: Install error - 0x800f0991

Question

Windows updates fail to install? Every update I get error codes.

Answer 1

Hi,

Typically a repair install works if all updates fail.

STEP 1:

"The first step would be to try resetting Windows updates using an automatic script.

Reset Windows updates in Windows 10/11

http://www.yourwindowsguide.com/2015/12/windows-update-complete-reset-in.html

Download the file > Right-click it and run as administrator. Reboot and check for updates again.

https://www.dropbox.com/s/ot1kwb78h3rpx3z/WuReset2.0.bat?dl=1

STEP 2: IF STEP 1 Didn't help:

"Please try a repair install as the next step. It keeps everything, including apps and files, and reinstalls Windows.

Repair Install Windows 11 using an ISO file

https://www.yourwindowsguide.com/2021/08/repair-install-windows-11-using-an-iso-file.html

1. Download Windows 11 ISO file from the following link:

https://www.microsoft.com/software-download/Windows11

2. Under Download ISO file, select Windows 11.
3. Click Download and choose the Language in which Windows is installed.
4. Click 64-bit Download to start the download.
5. When downloaded, open the ISO file, and run Setup.exe to start the upgrade."

Disclaimer:

Content in the above blog is written by a former Windows Insider MVP, so it is safe. Do watch out for the ads.

Answer 2

The error code 0x800f0991 typically indicates that a required payload file is missing during the installation of a Windows update. This can happen for various reasons, including issues with the Windows Update service or problems with the system files.

To resolve this issue, you can try the following steps:

1. Check for Corrupted System Files: Run the System File Checker tool by opening Command Prompt as an administrator and executing the command sfc /scannow. This will scan for and attempt to repair any corrupted system files.
2. Ensure Windows Update Services are Running: Make sure that the Windows Update service is running. You can check this in the Services application.
3. Reset Windows Update Components: You can reset the Windows Update components by following these commands in an elevated Command Prompt:

      net stop wuauserv
      net stop cryptSvc
      net stop bits
      net stop msiserver
      net start wuauserv
      net start cryptSvc
      net start bits
      net start msiserver
   

4. Check Disk Space: Ensure that your system has enough disk space available for the update to be installed.
5. Use the Windows Update Troubleshooter: You can run the built-in Windows Update troubleshooter to automatically find and fix some problems with Windows Update.

If these steps do not resolve the issue, consider checking the Windows Update logs for more detailed error messages that could provide additional insights into the problem.

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References:

• Error 0x800719e4 (ERROR_LOG_FULL) when Windows Update fails
• Windows Update common errors and mitigation