How to Fix KB5021255 Update Not Installing on Windows 11

Is the KB5021255 update not working, installed, or downloaded on Windows 11?

Windows released the update on December 13, 2022 (OS Build 22621.963).

The update fixes an issue with the Task Manager that displays elements in odd colors.

The issue occurs if you set “Choose your mode” to “Custom” in the personalization settings.

Various improvements were made like the Data Protection Application Programming Interface.

The issue is that the decryption of a certificate’s private key might fail which causes VPN and other certificate-based authentications to fail too.

In this guide, you’ll learn how to fix the installation/download issue for the KB5021255 update on Windows 11.

• Fix 1: Run the Update Troubleshooter
• Fix 2: Restart Windows Update and background intelligent transfer service
• Fix 3: Use Windows 11 Installation Assistant
• Fix 4: Use Microsoft Update Catalog
• Fix 5: Reset Windows Update components
• Fix 6: Use the Media Creation Tool

Fix 1: Run the Update Troubleshooter

1. Open the Windows start menu > Settings.
2. System > Troubleshoot > Other troubleshooters.
3. Windows Update > Run > Restart your PC.

Fix 2: Restart Windows Update and background intelligent transfer service

1. Windows search > Services.
2. Windows update > Startup type > Automatic > Apply > OK.
3. Select “Restart the service” for “Windows Update”.
4. Background intelligent transfer service > Startup type > Automatic > Apply > OK.
5. Select “Restart the service” for “Background intelligent transfer service”.
6. Restart your PC.

Fix 3: Use Windows 11 Installation Assistant

1. Go to https://www.microsoft.com/software-download/windows11.
2. Click on “Download Now”.
3. Run the .exe file > Accept and install.

Fix 4: Use Microsoft Update Catalog

1. Go to https://www.catalog.update.microsoft.com/Home.aspx.
2. Search for “KB5021255”.
3. Download the Windows 11 KB5021255 update.
4. Restart your PC.

Fix 5: Reset Windows Update components

Copy these and paste them into the Notepad app:

SC config trustedinstaller start=auto
net stop bits
net stop wuauserv
net stop msiserver
net stop cryptsvc
net stop appidsvc
Ren %Systemroot%\SoftwareDistribution SoftwareDistribution.old
Ren %Systemroot%\System32\catroot2 catroot2.old
regsvr32.exe /s atl.dll
regsvr32.exe /s urlmon.dll
regsvr32.exe /s mshtml.dll
netsh winsock reset
netsh winsock reset proxy
rundll32.exe pnpclean.dll,RunDLL_PnpClean /DRIVERS /MAXCLEAN
dism /Online /Cleanup-image /ScanHealth
dism /Online /Cleanup-image /CheckHealth
dism /Online /Cleanup-image /RestoreHealth
dism /Online /Cleanup-image /StartComponentCleanup
Sfc /ScanNow
net start bits
net start wuauserv
net start msiserver
net start cryptsvc
net start appidsvc

Save the file as “Wufix.bat” > set the location as desktop > All Files > Save.

Run the file as an administrator to restart all the Windows update services and restart your PC.

Fix 6: Use the Media Creation Tool

1. Go to https://www.microsoft.com/en-us/software-download/windows11.
2. Click on “Download Now”.
3. Follow the on-screen instructions.
4. Open the downloaded file.
5. Run the setup file.
6. Follow the on-screen instructions and complete the installation process.

Further reading

How to Fix KB5020044 Update Not Installing on Windows 11

How to Fix KB5020030 Update Not Installing on Windows 10

How to Fix KB5019980 or KB5020622 Update Not Installing on Windows 11