Windows 11 KB5065426 won’t install due to several errors, such as 0x800F0991, 0x800F0922, 0x80071A2D, 0x800F081F, and more. Additionally, we’re seeing reports of the Windows 11 September 2025 Update taking longer than usual to download (could be due to its large size) or a glitch. File sharing also appears to be affected in some cases.
KB5065426 is a mandatory patch rolling out as part of the Windows 11 September 2025 Update. This security patch is going to attempt installation every time Windows periodically scans for new updates. While it’s not exactly a deal breaker, I’ve had dozens of people texting me that the September 2025 Update just won’t install.
One user told me that they see 0x800F081F if they try to install KB5065426. But it’s not just limited to one particular error code. Based on reports spotted by Windows Latest, here is the list of errors you might see when installing Windows 11 KB5065426 (September 2025 Update):
- 0x800F0991
- 0x800F0922
- 0x80071A2D
- 0x800F081F
- 0x80070302
- 0x80070306
- 0x8000FFFF
I’ve several people sharing their side of how Windows update is not working out for the September release.
“I have used both SFC and DISM commands to ensure there are no corrupted files. The installation of Windows 11 KB5065426 always fails, and I get the ‘retry all’ button on Windows Update. I click that button and the download starts again and fails,” one user noted. “I downloaded the package and tried a manual install… the install failed, but I did not get an error. The installation package just completed with a ‘did not install’ message.
In our tests, we noticed that one of the Windows failures shows up as just “2025-09 Cumulative Update for Windows 11 Version 24H2 for x64-based Systems (KB5065426) (26100.6584). Download Error – 0x800700C1” on the Windows Update page.
A system admin with decades of experience also told me that Windows 11 KB5065426 just won’t install “no matter” what they do. What is interesting is that I’m getting a bunch of emails and texts from people who claim they never had any issues with Windows Update.
It’s the first time some people are running into different errors when downloading/installing the September 2025 Patch Tuesday.
“KB5065426 errors out when I try to install it on my PC. I’m getting ‘Install error – 0x800F0991’ no matter what I do, and let me tell you that I’m an experienced Windows OS admin,” a system admin told me in an email. Like I mentioned, it does appear to be a pain for a lot of people.
But what about using Microsoft Update Catalog? I’ve always recommended trying Update Catalog when Windows Update fails, but in the case of Windows 11 KB5065426, Update Catalogue might throw an error message. See the screenshot below. I tried to install the patch, and it throws the following error:
Windows Latest reader added that Microsoft Update Catalog doesn’t work as a workaround for the September 2025 Patch Tuesday.
“Tried downloading the file directly from the Catalog and whilst at first it runs to around 60% of the progress bar on the standalone installer. It too fails and reports the KB5065426 was not installed,” another tester wrote.
What to do if Windows 11 KB5065426 is not installing?
So, what can be done? Well, just use the Media Creation Tool and Windows 11 KB5065426, or other updates, and they will install successfully. I think the best part of using the Media Creation Tool is that it also patches other potential issues in the operating system.
To get started, download and install the Media Creation Tool from Microsoft’s download portal, but remember to select “Upgrade this PC” and that the toggle to keep personal files or pictures is selected.
Finally, Windows will reinstall, and you can check for updates. In some cases, Windows 11 KB5065426 will already be in download state, but if it’s not, just check for updates, and it will proceed smoothly.
If the Media Creation Tool isn’t working or you do not see the option to keep your files or folders, you can use the Update Assistant Tool instead.
I’ve reached out to Microsoft and also sources at the company, and I’ve told them about these installation errors. Given the past trend, we might see a server-side change that would help people in the coming days. Windows Latest has always shared bug reports with Microsoft, and we do see the company acting.
Windows 11 September 2025 Update issues affect file sharing and more
But installation errors aren’t the only problem we’ve spotted. We’re also seeing reports of broken file sharing on Windows 11 24H2 after KB5065426. People say SMB/network shares stop working between Windows 11 PCs, and they see “System error 86” or failed credential prompts.
In small offices, this affected many machines at once.
“After KB5065426 installed on 09-11 my two HP laptops with Win11 failed to connect to each other on the home network,” one of the affected users noted in a Feedback Hub post spotted by Windows Latest.
“Before the update, file sharing worked perfectly. Now I cannot connect to any file shares set up before or after the update. I have tried to uninstall this update on both of my machines, but it will not uninstall.”
In rare cases, some users lose internet entirely after the update, but I’m not seeing reports of widespread issues.
If you’re affected, you can open Settings > Windows Update > Update history > Uninstall updates, and select Windows 11 KB5065426 to uninstall it. Windows will warn that you’re going to remove the security patch. You can go ahead when you’re confident that your PC started having issues in September.
If you’re unable to remove it because you’re past the due time, just use the Media Creation Tool and refresh the Windows installation (do a clean install/in-place upgrade).
Always remember that you’re going to miss out on important security fixes and some new features, like Emoji 16 support, when the update is removed.
