Many Windows 11 users have reported that updates KB5066835 and KB5066128 fail to install. These updates may either download but not install, or the installation may stall and show error codes.
Common reasons include corrupted update files, software conflicts, or issues with Windows Update components. This guide provides step-by-step solutions to resolve these problems.
⚙️ Common Causes for Update Failure
- Corrupted Windows Update cache
- Antivirus or firewall blocking the installation
- Conflicting third-party software
- Low disk space or system errors
- Pending updates that haven’t been installed
- Issues with the update server or network
🛠️ Fix 1: Run Windows Update Troubleshooter
Windows has a built-in troubleshooter to automatically fix common update issues.
Steps:
- Press Windows + I → System → Troubleshoot → Other troubleshooters
- Locate Windows Update → Click Run
- Follow the on-screen instructions and apply any recommended fixes
- Restart your PC and try installing the update again
✅ Why it works: Detects and repairs broken update components automatically.
🛠️ Fix 2: Clear Windows Update Cache
Corrupted cache files can prevent updates from installing.
Steps:
- Press Windows + R → type services.msc
- Find Windows Update service → Right-click → Stop
- Navigate to:
C:\Windows\SoftwareDistribution\Download - Delete all files in the Download folder
- Go back to Services → Windows Update → Start
- Retry installing the update
✅ Why it works: Removes corrupted cached files that block installation.
🛠️ Fix 3: Use the DISM and SFC Tools
Corrupted system files may prevent updates from applying.
Steps:
- Press Windows + S → type cmd → Run as administrator
- Run the following commands one by one:
DISM /Online /Cleanup-Image /RestoreHealth sfc /scannow - Wait for the process to complete and restart your PC
- Try installing KB5066835 or KB5066128 again
✅ Why it works: Repairs system files required for updates to install properly.
🛠️ Fix 4: Manually Download and Install the Update
Sometimes installing the update manually works better than Windows Update.
Steps:
- Go to the Microsoft Update Catalog: https://www.catalog.update.microsoft.com
- Search for KB5066835 or KB5066128
- Download the version matching your system architecture (x64 or ARM)
- Double-click the downloaded file and follow the prompts
- Restart your PC after installation
✅ Why it works: Bypasses Windows Update and applies the patch directly.
🛠️ Fix 5: Disable Antivirus and Firewall Temporarily
Security software may interfere with update installation.
Steps:
- Temporarily disable third-party antivirus
- Open Windows Security → Firewall & Network Protection → Turn off firewall
- Try installing the update
- Re-enable security software after the update installs
✅ Why it works: Prevents security programs from blocking system updates.
🛠️ Fix 6: Reset Windows Update Components
If the problem persists, resetting update components can help.
Steps:
- Open Command Prompt as administrator
- Run the following commands one by one:
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 - Restart your PC and retry the update
✅ Why it works: Resets all update-related components to default, fixing persistent errors.
🛠️ Fix 7: Check Disk Space and System Health
Insufficient disk space or system errors may prevent updates.
Steps:
- Open Settings → System → Storage and ensure at least 10 GB free space
- Run chkdsk to check for disk errors:
chkdsk /f /r - Restart the PC and try the update again
✅ Why it works: Ensures there’s enough space and no disk errors blocking updates.
💡 Additional Tips
- Always restart your PC after each troubleshooting step
- Ensure you are connected to a stable internet connection
- Avoid installing updates during heavy system usage
- Keep other pending updates installed first
❓ FAQs
Q1: Why does KB5066835 or KB5066128 fail repeatedly?
A1: Common reasons include corrupted cache, antivirus interference, or missing system files.
Q2: Is it safe to install updates manually?
A2: Yes, downloading from Microsoft Update Catalog ensures a safe installation.
Q3: Can DISM and SFC fix update errors?
A3: Yes, they repair corrupted system files required for Windows Update.
🎯 Conclusion
If KB5066835 or KB5066128 is not installing on Windows 11 25H2/24H2, the problem usually stems from corrupted files, conflicting software, or broken update components. Using the steps above—running troubleshooters, clearing cache, repairing system files, or installing manually—you can resolve the issue and keep your PC fully updated.
✅ Apply these steps to install updates successfully and maintain system stability.
