2026-02 Security Update (KB5077181) (26200.7840) - update failed

Question

2026-02 Security Update (KB5077181) (26200.7840) - Update is getting failed due to
Install error - 0x800f0991

Answer 1

no 3rd party av

25H2 (OS build 26200.7171)

Answer 2

Hey, I have almost the same problem. I couldn't install the update (KB5077181) (26200.7840). I found online the solution, and I did it, and it worked. Now my version is 25H2 ( OS Build 26200, 7623 ), not 25H2 ( OS Build 26200, 7640 ), why? When I try to install the update from Windows Update, It show install error - 0x80070306

Answer 3

Hi. I'm David, and I'm happy to help you.

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Please clarify the following:

Do you have a third-party antivirus installed? If yes, which one?

Also. What is the current "OS Build" of your Windows 11?

• Press "Windows + R", type winver, and click OK.

If you prefer, share a screenshot. Use the shortcut "Windows + Shift + S" to use the screenshot tool.

Be sure to censor your email address if it appears. The Microsoft Q&A is public.

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I await your reply.

Answer 4

The error code 0x800f0991 typically indicates that the update is unable to install due to missing or corrupted files required for the installation. To resolve this issue, you can try the following steps:

1. Run the Windows Update Troubleshooter: This built-in tool can help identify and fix common issues with Windows Update.
2. Check for Missing Components: Ensure that the necessary components for the update are present. You may need to repair the Windows image using the DISM tool. Open Command Prompt as an administrator and run the following commands:
   • DISM /Online /Cleanup-Image /CheckHealth
   • DISM /Online /Cleanup-Image /ScanHealth
   • DISM /Online /Cleanup-Image /RestoreHealth
3. Reset Windows Update Components: Sometimes, resetting the Windows Update components can help resolve installation issues. You can do this by stopping the Windows Update service, renaming the SoftwareDistribution and Catroot2 folders, and then restarting the service.
4. Manually Install the Update: If the above steps do not work, you can manually download and install the update from the Microsoft Update Catalog using the KB number.
5. Check System Files: Run the System File Checker tool by executing sfc /scannow in an elevated Command Prompt to repair any corrupted system files.

After performing these steps, try to install the update again. If the issue persists, consider reaching out to Microsoft Support for further assistance.