How to fix Windows update error 0x800f0991?

Install error 0x800f0991 means Windows Update downloaded a cumulative update but could not install it, because a file the update depends on is missing on the PC. It hit many Windows 11 PCs with KB5065426 (build 26100.6584) and still appears with later updates. Restart, check for updates again, then install the update by hand.

Facts checked on 15 October 2026. Steps written for Windows 11 (24H2, 25H2 and 26H2).

What install error 0x800f0991 means

0x800f0991 is an error of Component-Based Servicing, the part of Windows that installs updates. It is not a download error and not a network error. The update arrived on the PC, and Windows stopped while it was putting the new system files in place.

Microsoft Learn gives the code the name PSFX_E_MISSING_PAYLOAD_FILE and says it is "associated with update sequencing or dependency errors". Read plainly: the update needs a file (the payload) from an earlier update or from Windows itself, and that file is not where it should be.

Why Windows update error 0x800f0991 appears

The causes below are ordered from the most likely to the least likely. Each one is tied to the fix that deals with it.

The first row is documented. PCWorld reported on 16 September 2025 that KB5065426 would not install for some users, with 0x800F0991 first in a list that also had 0x800F0922, 0x80071A2D and 0x800F081F. For some of them even the package from the Microsoft Update Catalog failed.

The second row is a report, not a Microsoft statement. In a solved Sysnative thread from October 2025, KB5070773 failed with 0x800f0991 on Windows 11 25H2 although SFC and DISM found no errors. The analyst found the line Matching binary snapshot_support.dll missing for component UserExperience-AIX in CBS.log.

Where CBS.log is and which line explains 0x800f0991

You do not need the log for Fix 1 and Fix 2. Read it when they did not help: the log names the missing file, and that tells you whether a manual install or a repair is your next step.

1. Press Win + R, type %systemroot%\Logs\CBS and press Enter.
2. Copy CBS.log to the Desktop and open the copy in Notepad, so the original stays untouched.
3. Press Ctrl + F and search for 0x800f0991. Note the time of the last hit.
4. Search for Matching binary and for , Error near that time.
5. Write down the file name and the component name from that line. They are what support will ask for.

• Microsoft Learn says to check CBS.log and the older CbsPersist_*.log and CbsPersist_*.cab files in the same folder. A .cab file opens like a folder in File Explorer.
• A Matching binary line with a file name points to Fix 2, then Fix 3.
• The words ERROR_SXS_COMPONENT_STORE_CORRUPT or mark store corrupt point to Fix 3, then Fix 6.
• No clear line at all: go through the fixes in order.

How to fix Windows update error 0x800f0991

Fix 1 and Fix 2 are aimed at this code and help most readers. Fix 3 to Fix 5 are the general repairs, each in short form with the full procedure linked. Fix 6 and Fix 7 reinstall Windows over itself and keep your apps and files: Microsoft names this as the reliable repair for this family of servicing errors.

Fix 1. Restart the PC and check for updates again

5 to 20 minutesNo riskAlways first, and above all when the error appeared with a new monthly update.

A restart finishes servicing work that is waiting on files in use. Cumulative updates also replace each other, so a newer update offered after the restart can install where the old one failed.

1. Save your work and select Start > Power > Restart. Use Restart, not Shut down.
2. Open Settings > Windows Update and select Check for updates.
3. Install everything that is offered. If the failed update is still listed, select Retry next to it.
4. If it fails again, restart one more time and repeat the check once.
5. Open Settings > Windows Update > Update history and see whether the update is now listed as installed.

Fix 2. Install the update by hand with DISM from the Microsoft Update Catalog

20 to 40 minutesLow riskOne cumulative update keeps failing, and SFC and DISM report no damage.

The catalog gives the full package instead of the small pieces Windows Update sends, so the files missing on the PC come with it. In the Sysnative case this was the fix: the analyst had the user put the update and KB5043080 in C:\MSU and install it with DISM, and it installed.

1. Check your Windows version. Press Windows key + R, type winver and press Enter. Note the version (for example 25H2) and the OS build.
2. Find the KB number. Open Settings > Windows Update. A failed or pending update is listed with its KB number; earlier ones are under Update history.
3. Check the processor type. Open Settings > System > About and look at System type: an x64-based PC needs the x64 file, an ARM-based PC (for example Snapdragon) needs the arm64 file.
4. Search the catalog. Open the Microsoft Update Catalog at catalog.update.microsoft.com in your browser, type the KB number (for example KB5124010) in the search box and press Enter.
5. Pick the right row. Find the row whose title names your Windows version and your processor type (x64-based or arm64-based) and select Download on that row.
6. Download every file listed. A window lists one or more .msu links. Download all of them into one empty folder, for example C:\packages. On Windows 11 24H2 and later the list can include earlier checkpoint updates that the new one needs.
7. Install a single file. If there is only one file, double-click it and confirm the installation in the Windows Update Standalone Installer.
8. Install several files with DISM. If there are several files, open an elevated Terminal or Command Prompt and run DISM with the newest file. DISM finds the other files in the same folder and installs them in the right order.

   DISM /Online /Add-Package /PackagePath:C:\packages\<newest-file>.msu

9. Restart. Restart the PC when the installation finishes, then run winver again: the OS build should have changed.

These steps were written for Windows 11 24H2 and later; Windows 10 22H2. The full page with the other versions and what each result means: Install an update from the Microsoft Update Catalog

1. Create the folder C:\MSU and save the downloaded .msu files there. If the catalog offers more than one file for the update, save all of them.
2. Right-click Start and select Terminal (Admin). Select Yes when Windows asks for permission.
3. Install the update with DISM. Replace the file name with the name of your file:

   DISM /Online /Add-Package /PackagePath:C:\MSU\windows11.0-kbXXXXXXX-x64.msu

4. Wait until DISM says The operation completed successfully. and restart the PC.
5. Press Win + R, type winver and press Enter. The build number should now be the one of the new update.

Fix 3. Repair the component store with DISM and SFC

15 to 40 minutesNo riskCBS.log names a missing file, 0x80073712 also appears, or Fix 2 failed with the same code.

The update failed because a file in the component store is missing. DISM with RestoreHealth downloads clean copies of damaged components, and SFC then repairs the system files built from them.

1. Open an elevated command window. Right-click Start and select Terminal (Admin), or type cmd in the search box, right-click Command Prompt and select Run as administrator. Select Yes when Windows asks for permission.

   

2. Run DISM first. Type the command below and press Enter. DISM downloads clean copies of damaged components from Windows Update, so it can take several minutes. Wait until it says The operation completed successfully.

   DISM.exe /Online /Cleanup-Image /RestoreHealth

   

3. Run System File Checker. In the same window, type the command below and press Enter. Do not close the window until the verification reaches 100%.

   sfc /scannow

   

4. Read the result and restart. Compare the last message with the table below this guide, then restart the PC so that repaired files are loaded.

   

These steps were written for Windows 11 24H2 and 25H2. The full page with the other versions and what each result means: Run DISM and SFC to repair Windows system files

Fix 4. Run the Windows Update troubleshooter

5 minutesNo riskYou do not want to type commands, or the fixes above changed nothing.

The troubleshooter checks the update services and clears a stuck attempt. It cannot put back a missing payload file, but it is free of risk and rules out the simple cases before a reinstall.

1. Open Troubleshoot settings. Select Start > Settings > System > Troubleshoot.
2. Open the list of troubleshooters. Select Other troubleshooters.

   

3. Run the Windows Update troubleshooter. Under Most frequent, select Run next to Windows Update. The Get Help app opens and starts the checks.

   

4. Read the result. Wait until Get Help finishes. If it found and fixed a problem, it says so and asks whether this solved the problem. Answer the question so it can offer the next step.

   

5. Restart the PC. Restart when the troubleshooter finishes, even if it does not ask you to.
6. Check for updates again. Select Start > Settings > Windows Update > Check for updates, and install the updates it finds.

These steps were written for Windows 11 (screenshots: 26H2). The full page with the other versions and what each result means: Run the Windows Update troubleshooter

Fix 5. Reset the Windows Update components and the update cache

10 minutesLow riskThe update fails at once at the same point, and the earlier fixes did not help.

A damaged download in the SoftwareDistribution folder is used again at every retry. Stopping the update services and renaming the folder makes Windows download the update from scratch. It does not repair the component store.

1. Open Command Prompt as administrator. Type cmd in the search box, right-click Command Prompt and select Run as administrator. Select Yes when Windows asks for permission.
2. Stop the update services. Type the commands below and press Enter after each one. If Windows says that other services depend on Cryptographic Services, it stops them too. A message that a service is not started is fine.

   net stop wuauserv
   net stop bits
   net stop cryptsvc

3. Delete the download queue files. This clears the list of downloads that the Background Intelligent Transfer Service keeps. If Windows says it cannot find the files, continue.

   del "%ALLUSERSPROFILE%\Application Data\Microsoft\Network\Downloader\qmgr*.dat"

4. Rename the update cache folders. Renaming keeps a copy in case you need it; Windows creates new, empty folders when the services start again. If you get Access is denied, a service is still running: repeat the previous step.

   ren %systemroot%\SoftwareDistribution SoftwareDistribution.old
   ren %systemroot%\System32\catroot2 catroot2.old

5. Start the services again. Type the commands below and press Enter after each one. The requested service has already been started is fine: Windows started it on its own.

   net start cryptsvc
   net start bits
   net start wuauserv

6. Restart and check for updates. Restart the PC. Then select Start > Settings > Windows Update > Check for updates. The first check can take longer than usual because everything is downloaded again.

These steps were written for Windows 11 and Windows 10 (the steps are the same). The full page with the other versions and what each result means: Reset Windows Update components

Fix 6. Reinstall Windows over itself with Fix problems using Windows Update

1 to 2 hoursLow riskNothing above worked, or the CBS log shows damage that DISM could not repair.

The reinstall puts a clean copy of your current Windows in place, so the missing payload files are back. Microsoft Learn names an in-place reinstall as the only reliable resolution for this group of servicing errors, including 0x800F0991.

1. Open Recovery in Settings. Open Settings > System > Recovery. Next to Fix problems using Windows Update, select Reinstall now. This keeps your apps, files and settings.

   

2. Start the reinstall. Choose whether the PC may restart on its own 15 minutes after the installation, then select OK.
3. Wait and restart. Windows Update downloads and installs a repair copy of your current Windows version. Keep the PC plugged in and online, and restart it when asked.

These steps were written for Windows 11 22H2 and later. The full page with the other versions and what each result means: Reinstall Windows without losing files

• Keep the PC plugged in and online for the whole reinstall.
• The option is in Settings > System > Recovery. It can be missing on a PC managed by work or school.
• After the reinstall, open Settings > Windows Update and install the update that failed.

Fix 7. Run an in-place upgrade with Windows 11 setup and keep your files

1 to 2 hoursLow riskFix 6 is missing or failed, or you want to move to the newest Windows 11 version at the same time.

Setup replaces every system component and keeps your data, apps and settings. PCWorld relayed the Media Creation Tool or the Update Assistant as the workaround that got KB5065426 past 0x800f0991.

1. Back up the files you cannot lose, as in Fix 6.
2. Open Microsoft's Windows 11 download page and download the Installation Assistant, or the ISO under Download Windows 11 Disk Image (ISO).
3. With the ISO: double-click it to open it as a drive and run setup.exe. With the Installation Assistant: run it and follow it.
4. When setup asks what to keep, select Keep personal files and apps.
5. Leave the PC on and online until it restarts into Windows.
6. Open Settings > Windows Update and select Check for updates.

Microsoft Learn describes the same command for servers as setup.exe /auto upgrade /dynamicupdate disable. On a home PC the normal setup window does the same job.

If error 0x800f0991 is still there

When the in-place upgrade did not help or could not start, the next step depends on who manages the PC and what CBS.log says.

• What to send to support: the exact code, the KB number, the build from winver, the time of the last failed attempt and CBS.log.
• Which fixes you already ran, and the last line DISM printed.
• This is not a hardware fault in itself. The exception is a drive that reports errors in chkdsk: a failing drive damages the store again after every repair.

How to keep error 0x800f0991 from coming back

Windows 10 left support on 14 October 2025. A Windows 10 PC that stops installing updates is better moved to Windows 11 with the in-place upgrade in Fix 7, if its hardware allows it.

Frequently asked questions

What does error 0x800f0991 mean?

It means Windows could not install an update because a file the update depends on is missing. Microsoft Learn gives the code the name PSFX_E_MISSING_PAYLOAD_FILE and ties it to update sequencing or dependency errors. The download is fine and the internet connection is not the cause. The fault is in the component store, the folder of system components that every update builds on. CBS.log usually names the missing file a few lines before the error, in a line that starts with Matching binary.

Why does KB5065426 (26100.6584) fail with install error 0x800f0991?

KB5065426 is the Windows 11 24H2 security update of 9 September 2025, OS build 26100.6584. Within a week PCWorld reported that it would not install for some users, with 0x800F0991, 0x800F0922, 0x80071A2D, 0x800F081F and other codes. For some even the package from the Microsoft Update Catalog failed, and the workaround that was reported was the Media Creation Tool or the Update Assistant. Newer updates have replaced KB5065426 since then, so restart and check for updates first, then use Fix 2 or Fix 7.

Why does SFC and DISM find nothing while the update still fails with 0x800f0991?

Because the missing file is not one that SFC checks, and DISM can see the store as healthy when one payload file is gone. In a solved Sysnative case, KB5070773 failed with 0x800f0991 on Windows 11 25H2, and both tools reported no errors. CBS.log showed that snapshot_support.dll was missing for one component. Installing the update with DISM from the downloaded .msu file, with KB5043080 in the same folder, fixed it. That is Fix 2 on this page.

Is 0x800f0991 a known issue that Microsoft will fix?

Not as a published known issue. We found no Microsoft release health entry for this code on 15 October 2026. Microsoft Learn lists 0x800F0991 among servicing errors where an in-place upgrade is the reliable repair, in an article written for Azure virtual machines. For a home PC that means the fault is on the PC, not in one update. Microsoft will not send a fix for it, and the repair is Fix 2, Fix 3 or a reinstall that keeps your files.

Can I update to Windows 11 25H2 when I get 0x800f0991?

Yes, an in-place upgrade is one of the repairs. When the monthly update fails with 0x800f0991, run Windows 11 setup from Microsoft's download page and choose Keep personal files and apps, as in Fix 7. Setup puts a complete copy of Windows in place, so the missing payload file is replaced, and the PC comes out on the newest version. Back up your files first and keep the PC plugged in. After setup, check for updates again.

Do I lose my files with Fix problems using Windows Update or an in-place upgrade?

No. Both reinstall Windows and keep your apps, files and settings, when you choose to keep them. This is different from Reset this PC, which removes your apps even when you keep your files. Still, back up the files you cannot lose before any repair of Windows. A power cut during a reinstall is the main risk, so keep a laptop on its charger. Plan for one to two hours, because Windows downloads a full copy of itself.

Does error 0x800f0991 appear on Windows 10?

It can, because Windows 10 uses the same servicing stack, but the reports we read are almost all about Windows 11 24H2 and 25H2. The fixes are the same: restart, install the update by hand, then DISM and SFC, then an in-place upgrade. Windows 10 left support on 14 October 2025. A Windows 10 PC with this error is a good moment to move to Windows 11 with Fix 7, if the hardware allows it.

Is it safe to skip the update and ignore the error?

Not for long. The update that fails is the monthly cumulative update, which carries the security fixes for Windows. A PC with this error usually fails the next month's update too, because the missing file is still missing. One or two weeks while you work through the fixes is fine. Pausing updates for months to stop the message leaves the PC open to the problems those updates close.

Is this page the same answer for erreur d'installation, errore di installazione or erro de instalação 0x800f0991?

Yes. The code is the same in every language of Windows: only the words in front of it are translated. Erreur d'installation, errore di installazione, erro de instalação, error de instalación and installatiefout all mean install error, and the fixes are the same. The menu names in the steps are the English ones. In another display language, follow the position of the items: Settings, then Windows Update, then the button that checks for updates. The commands are typed the same way on every PC.