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

HGTaylor · Oct 24, 2025

Each time I try to install the update I get error message
"Install error - 0x800f081f"

Can anyone advise me, please?

[Thought should deal with the update before asking for guidance regarding a very slow boot up.]

OAT · Oct 24, 2025

HGTaylor said:
Each time I try to install the update I get error message
"Install error - 0x800f081f"

Can anyone advise me, please?

[Thought should deal with the update before asking for guidance regarding a very slow boot up.]

You are apparently not the only one. The article offers a solution though.

Microsoft confirms Windows 11 KB5066835 issues. Localhost, File Explorer preview, install errors

Windows 11 KB5066835 is causing the following issues: a bug that blocks lockhost connection, File Explorer preview pane and more.

www.windowslatest.com

HGTaylor · Oct 24, 2025

Each time I try to install the update I get error message
"Install error - 0x800f081f"

I am running Windows 11 Home, Version 24H2, OS build 26100.6584. Other details are in my profile here on Windows 11 Forum - per 'My Computer' link below in this post.

Can anyone advise me, please?

[Thought should deal with the update before asking for guidance regarding a very slow boot up.]

glasskuter · Oct 24, 2025

See windows update troubleshooting steps listed here.

Windows 11 Update Error

Windows 11 24H2 Insider Build (Beta Channel). Cannot install Windows 11 Insider Preview Quality Update (26120.6972): Install error - 0x800f0922 The above update won't install. I've tried everything I know, including manually resetting Windows Update components, SFC reports zero integrity...

www.elevenforum.com

HGTaylor · Oct 24, 2025

OAT said:
You are apparently not the only one. The article offers a solution though.

Microsoft confirms Windows 11 KB5066835 issues. Localhost, File Explorer preview, install errors

Windows 11 KB5066835 is causing the following issues: a bug that blocks lockhost connection, File Explorer preview pane and more.

www.windowslatest.com

Thank you, OAT. I visited link but some of what I read was not clear to me as to what to do or whether to do nothing at the moment. My laptop is set to 'auto download and update' but obviously there is an overriding issue

.

RFS · Oct 24, 2025

I've had this 2 or 3 times on previous updates. Best way to resolve it is to do a repair update which is run by Windows Update thus -

Settings -> windows update -> advanced options -> recovery -> fix problems using windows update.

OAT · Oct 24, 2025

HGTaylor said:
Thank you, OAT. I visited link but some of what I read was not clear to me as to what to do or whether to do nothing at the moment. My laptop is set to 'auto download and update' but obviously there is an overriding issue.

Since you are on 24H2, you need to install the 1st .msu on the list from the update catalog:

Microsoft Update Catalog

Once downloaded, run the .msu file.

HGTaylor · Oct 24, 2025

OAT said:
Since you are on 24H2, you need to install the 1st .msu on the list from the update catalog:

Microsoft Update Catalog
Once downloaded, run the .msu file.

Again, thank you, OAT.
I used the 'catalog' link you gave and I clicked to download of 1st item (per attatched JPG file) of the 5 in the 'cumulative' update list.

Per attached JPG file, the 1st item is a list that contains links to 2 '.msu' files and I have downloaded both of the '.msu' files.

Do I now run both '.msu' files one after the other, please?

OAT · Oct 24, 2025

HGTaylor said:
Again, thank you, OAT.
I used the 'catalog' link you gave and I clicked to download of 1st item (per attatched JPG file) of the 5 in the 'cumulative' update list.

Per attached JPG file, the 1st item is a list that contains links to 2 '.msu' files and I have downloaded both of the '.msu' files.

Do I now run both '.msu' files one after the other, please?

My apologies as I made you waste time downloading the wrong files.

It is actually the third option you need to get since you do not have an ARM64 system.
Had you tried to run any of those two, it would have warned you that it was not appropriate for your device.
Please delete these in order to avoid confusion.

So, after downloading again,you will end up indeed with 2 .msu, run the lower number KB first.

1- windows11.0-kb5043080-x64_953449672073f8fb99badb4cc6d5d7849b9c83e8.msu
2- windows11.0-kb5066835-x64_2f193bc50987a9c27e42eceeb90648af19cc813a.msu

Helmut · Oct 24, 2025

Just leave it, there are errors in that one, fortunately for you it is not installing.

If you do install it there is a follow up corrective out of band update, which does not install on mine (KB5070773) (26200.6901)

October 20, 2025—KB5070773 (OS Builds 26200.6901 and 26100.6901) Out-of-band - Microsoft Support

support.microsoft.com

HGTaylor · Oct 24, 2025

OAT said:
My apologies as I made you waste time downloading the wrong files.

It is actually the third option you need to get since you do not have an ARM64 system.
Had you tried to run any of those two, it would have warned you that it was not appropriate for your device.
Please delete these in order to avoid confusion.

So, after downloading again,you will end up indeed with 2 .msu, run the lower number KB first.

1- windows11.0-kb5043080-x64_953449672073f8fb99badb4cc6d5d7849b9c83e8.msu
2- windows11.0-kb5066835-x64_2f193bc50987a9c27e42eceeb90648af19cc813a.msu

Thank you, again, OAT.
Had I looked closely at what I was doing I could have assisted you

Sorry.
I am grateful for your guidance.

I have set about the new downloads and I will let you know the outcome(s) - and after that also ask if there is more to do to complete update 'KB5066835 26100.6899'.

HGTaylor · Oct 24, 2025

Helmut said:
Just leave it, there are errors in that one, fortunately for you it is not installing.

If you do install it there is a follow up corrective out of band update, which does not install on mine (KB5070773) (26200.6901)

October 20, 2025—KB5070773 (OS Builds 26200.6901 and 26100.6901) Out-of-band - Microsoft Support

support.microsoft.com

Hello, Helmut.

To whom was/is your "Just leave it ..." message addressed, please?

FrancoDT · Oct 24, 2025

HGTaylor said:
Hello, Helmut.

To whom was/is your "Just leave it ..." message addressed, please?

Build KB5066835 26100.6899 has numerous bugs/issues so go with the fix 26100.6901. Also the easiest workaround for WU install errors is what RFS posted earlier Settings -> windows update -> advanced options -> recovery -> fix problems using windows update.

HGTaylor · Oct 24, 2025

FrancoDT said:
Build KB5066835 26100.6899 has numerous bugs/issues so go with the fix 26100.6901. Also the easiest workaround for WU install errors is what RFS posted earlier Settings -> windows update -> advanced options -> recovery -> fix problems using windows update.

Thank you for your notes, FrancoDT.
My technical knowledge is limited so I would want to avoid using 'workaround'.

Presently I do not have 'build KB5066835 26100.6899' installed.
From your note, it seems that if I install 'build KB5066835 26100.6899', I will need to install the official '26100.6901' fix.

FrancoDT · Oct 24, 2025

HGTaylor said:
Thank you for your notes, FrancoDT.
My technical knowledge is limited to I would not want to use 'workaround'.

Presently I do not have 'build KB5066835 26100.6899' installed.
From your note, it seems that if I install 'build KB5066835 26100.6899', I will need to install the official '6100.6901' fix.

If WU offers it that's the easiest way to get it. By workaround I mean the built in settings repair install is the easiest and least complicated fix. It's the preferred way to get the update that keeps giving installation errors like 0x800f081f and other common ones.

Helmut · Oct 24, 2025

HGTaylor said:
Hello, Helmut.

To whom was/is your "Just leave it ..." message addressed, please?

Of course it was addressed to you. post #10 and more importantly the bit you edited out, the MS reference.

Spunk · Oct 24, 2025

HGTaylor said:
Thought should deal with the update before asking for guidance regarding a very slow boot up

Your drive may have bad sectors and starting to fail.
Download DiskGenius or Crystal Disk Info both in my signature.
View the SMART Info on the drive (s) if it is less than GOOD the drive needs to be replaced.

HGTaylor · Oct 25, 2025

OAT said:
My apologies as I made you waste time downloading the wrong files.

It is actually the third option you need to get since you do not have an ARM64 system.
Had you tried to run any of those two, it would have warned you that it was not appropriate for your device.
Please delete these in order to avoid confusion.

So, after downloading again,you will end up indeed with 2 .msu, run the lower number KB first.

1- windows11.0-kb5043080-x64_953449672073f8fb99badb4cc6d5d7849b9c83e8.msu
2- windows11.0-kb5066835-x64_2f193bc50987a9c27e42eceeb90648af19cc813a.msu

Hello, OAT.
Your guidance is clear to understand and to follow, with my limited knowledge.

I have downloaded the two .msu files ready for double clicking to run the "...kb5043..." .msu file first.

I have gotten other guidance in this thread that is not as clear to me as yours. Before I run the first .msu I ask please that, when you have time, you look through the other guidance offered to me in this thread, then offer me your further direction, please.

HGTaylor · Oct 25, 2025

Helmut said:
Of course it was addressed to you. post #10 and more importantly the bit you edited out, the MS reference.

Thank you very much, Helmut, for offering me guidance.

I already begun following guidance offered to me in this thread by OAT. If you think following the OAT guidance has problems, I will be very grateful if you raise the point with OAT, please.

HGTaylor · Oct 25, 2025

Spunk said:
Your drive may have bad sectors and starting to fail.
Download DiskGenius or Crystal Disk Info both in my signature.
View the SMART Info on the drive (s) if it is less than GOOD the drive needs to be replaced.

Thank for your note, Spunk, although in this thread we should deal with the Win-update issue. I will make a note of "Disk Genius" and "Crystal Disk" and view the "SMART info". I will feedback to you separately — but not in this thread.

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