Getting this error when installing windows update. Install error - 0x800f0991

Question

Getting this error when installing windows update.

Update

2025-10 Cumulative Update for Windows 11 Version 24H2 for x64-based Systems (KB5066835) (26100.6899)

Error

Install error - 0x800f0991

Answer 1

Hi, good day!

Please let me know if you have tried the methods below.

• Disable or uninstall any third-party VPN and Antivirus program to prevent it from interfering with the update.
• Run the Windows Update Troubleshooter Open Settings > System > Troubleshoot > Other troubleshooters > Windows Update > Run troubleshooter
• Make sure Windows Update and Background Intelligent Transfer services are available and running.

Press Windows key+R to open Run then type: services.msc

Press Enter to open Services app

Double-click Background Intelligent Transfer Service.

If the Startup status lists Stopped, click Start and then click OK. If the status is Running, right click then select Restart

Double-click Windows Update.

If the Startup status lists Stopped, click Start and then click OK. If the status is Running, right click then select Restart

• Please try to run SFC and DISM to check for any system errors and corrupted files. https://support.microsoft.com/windows/using-system-file-checker-in-windows-365e0031-36b1-6031-f804-8fd86e0ef4ca
• Reset Windows Update components manually https://www.elevenforum.com/t/reset-windows-update-in-windows-11.3808/ After that, restart your computer
• Here's a direct download link of KB5066835 from Microsoft Update Catalog. Download and install the update manually. https://catalog.sf.dl.delivery.mp.microsoft.com/filestreamingservice/files/7c0d1a12-9944-4b26-bed7-a722c040d631/public/windows11.0-kb5066835-x64_2f193bc50987a9c27e42eceeb90648af19cc813a.msu

If the issue persists, open Settings > System > Recovery.

Few things to check on the PC

• Unplug all external peripherals except for the Mouse, Keyboard, and LAN cable before starting
• Disable or uninstall any third-party Antivirus program to prevent it from interfering with the upgrade

Under Fix problems using Windows Update, click Reinstall Now

Once completed, your system will restart.

I look forward to receiving your update and I'm willing to collaborate with you till we resolve the issue. Do keep me informed by clicking "Add comment" below.

Answer 2

Try to download the windows update manually

Go to the Microsoft Update Catalog

Search for KB5066835.

Download the version matching your system (x64).

then try