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Install error - 0x800f0991 when trying to install this update2025-09 Cumulative Update Preview for Windows 11, version 25H2 for x64-based Systems (KB5065789) (26200.6725)

Michael Lennox 20 Reputation points
2025-10-12T14:35:33.92+00:00

when trying to install this update -

2025-09 Cumulative Update Preview for Windows 11, version 25H2 for x64-based Systems (KB5065789) (26200.6725)

am getting :- Install error - 0x800f0991

Windows development | Internet Information Services
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  1. Fred Moaven 5 Reputation points
    2025-10-16T17:06:28.6866667+00:00

    I've tried all the steps above, but I'm still getting the update error "Failed to install on ‎10/‎16/‎2025 - 0x800f0991". The Windows Update troubleshooter also failed :(

    The Windows Update diagnostic failed to run

    I'm sorry.  I was unable to run the Windows Update diagnostic. I might need to transfer you to an agent to help solve your problem. 

    1 person found this answer helpful.
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  2. FALAH FAKHRI 5 Reputation points
    2025-10-17T06:57:55.9966667+00:00

    I did follow the same answer and instructions, However, the same error, I got. Windows 11 pro

    1 person found this answer helpful.
  3. Tom Tran (WICLOUD CORPORATION) 1,920 Reputation points Microsoft External Staff
    2025-10-13T07:53:06.8+00:00

    Hi @Michael Lennox ,

    Thank you for sharing the details!

    From my understanding, the error 0x800f0991 is associated with CBS_E_STORE_CORRUPTION or component store corruption in the Windows servicing stack. This usually indicates that the update process cannot proceed because the underlying system files or the component store (used by Windows Update and DISM) is damaged or inconsistent. Common causes include:

    • Corrupted system files or component store.
    • Pending updates or restart required.
    • Interference from third-party antivirus or optimization tools.
    • Rarely, low disk space or resource issues.

    Here are a few steps you could try:

    Run DISM and SFC Repairs

    Open Command Prompt (Admin) and run:

    DISM /Online /Cleanup-Image /RestoreHealth
sfc /scannow

    These commands repair the component store and system files.

    Clear Windows Update Cache

    Stop the Windows Update service:

    net stop wuauserv
net stop bits

    Delete contents of C:\Windows\SoftwareDistribution\Download. Restart services:

    net start wuauserv
net start bits

    Use Windows Update Troubleshooter

    • Go to Settings > System > Troubleshoot > Other troubleshooters > Windows Update.

    Manual Installation

    • Download the update from Microsoft Update Catalog and install it manually.

    Check for Pending Restart

    • Restart your PC before retrying the update.

    The link shared points to the official Windows 11 installation media page. This is not a direct fix but can be used for an in-place upgrade (repair install). This process reinstalls Windows while keeping your files and apps intact, replacing corrupted system components and the servicing stack. It’s typically recommended when:

    • DISM/SFC and other steps fail
    • Updates repeatedly fail due to deep corruption

    For more details, please check out these documents:

    If these steps help, please let me know.

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