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

Question

The latest Windows update: 2025-10 Cumulative Update for Windows 11 Version 24H2 for x64-based Systems (KB5066835) (26100.6899) is failing to install, with install error 0x800f0991

I ran DISM and SFC and tried again, and once more. But this update is failing.

This is the first time that a Cumulative Windows 11 update has failed for my system.

It seems that there is a large number of Windows users for whom this update is not installing.

Any idea what is going on?

Answer 1

Sorry, no, it only appeared to help. Now Windows is trying once more to download and install KB5066835. I will need to wait and see if it succeeds this time.

Answer 2

It failed again with the same error

Answer 3

Greetings!

I'm Christine, I'll be happy to assist you. Sorry to hear that you're getting error when installing Windows updates. This error usually means that the file needed is damaged or corrupted. No worries, I'll do my best to help you.

Have you tried to run the Troubleshooter already?

Please follow the steps below:

1. Windows Update Troubleshooter

Windows 11

Please Click Start menu and type Troubleshoot

Hit Other troubleshooters

And select Windows Update

Finally, Run the troubleshooter

Please check if the issue persists

2. Please click Start menu and type CMD, right click on it and choose Run as Admin, please paste the command below and hit enter. (I understand that you did it already, but please do it one more time)

DISM.exe /Online /Cleanup-image /Scanhealth

DISM.exe /Online /Cleanup-image /Restorehealth

Please wait for it to finish and repair the system files.

Once done, please paste the command below and hit enter.

sfc /scannow

Please wait to finish.

Check if the issue persists.

3. Reset Windows update services:

Please click start menu and type cmd, right click on it and choose run with admin

Kindly copy and paste the command lines below and hit enter:

net stop wuauserv

net stop cryptSvc

net stop bits

net stop msiserver

Ren C:\Windows\SoftwareDistribution SoftwareDistribution.old

Ren C:\Windows\System32\catroot2 Catroot2.old

net start wuauserv

net start cryptSvc

net start bits

net start msiserver

Please check if the issue persists.

4. Please try to perform an in place upgrade. In place upgrade will install the new features or updates of Windows it will also fix corrupted system files. Kindly check the steps below:

Video on how to perform in place upgrade:

https://www.youtube.com/watch?v=CAOwN68AInE&feature=youtu.be

Please go to https://www.microsoft.com/en-us/software-download/windows11

Look for Download Windows 11 Disk Image and select Windows 11 (multi-edition ISO)

• Once you're able to download the ISO, please right click and open it
• Please look setup.exe and run it
• Select yes if you will will be asked for User Control
• Choose Next to Continue
• Please read the License Agreement and once done, hit Accept
• Please wait until the setup program is done and it will check if your device space is enough for the update
• You will see the Ready to install page, please ensure that the Keep personal files and apps has been checked.
• Lastly, click INSTALL and follow the prompt.
• It will restart your device several times, please wait for it to finish.

This may take sometime depends on your connection or the performance of your device.

Please let me know the result. I'll be happy to assist you all the way until it's resolved.

Thank you,

Christine L

Independent Advisor

Standard Disclaimer: Youtube.com link is a non-Microsoft website. The pages appear to be providing accurate, safe information. Watch out for ads on the sites that may advertise products frequently classified as PUP (Potentially Unwanted Products). Thoroughly research any product advertised on the sites before you decide to download and install it.

Answer 4

Yes, that actually helped.

It was your Step 3 that did the trick!

Thank you!

Answer 5

Alrighty. Please let me know how it goes.