install failed 2026-05 .NET Framework Security Update (KB5087051)

Question

May 2026 security update fails to install with error 0x800f0920. I cannot find ANY resources for this error code. I have attempted the update FIVE times without success. I have run DISM and SFC and there are NO errors. I'm running Windows 11 Pro 25H2 26200.8246. I have a Dell Optiplex i7-14700 with 64GB of RAM and a 2TB SSD drive. Can anyone help me?

Answer 1

Hi, I'm Bernard. I'm happy to help!

This issue occurs when there is a miscalibration with the Windows Update components. To sort out the issue, kindly follow the steps below:

Reset Windows Update components:

Open Terminal (Admin) or Windows PowerShell(Admin) (Press Windows key + X then click Terminal(Admin))

Copy each line of command, then press Enter (one line at a time)

net stop bits
net stop wuauserv
net stop appidsvc
net stop cryptsvc
Del "%ALLUSERSPROFILE%\Application Data\Microsoft\Network\Downloader\*.*"
rmdir %systemroot%\SoftwareDistribution /S /Q
rmdir %systemroot%\system32\catroot2 /S /Q
regsvr32.exe /s atl.dll
regsvr32.exe /s urlmon.dll
regsvr32.exe /s mshtml.dll
netsh winsock reset
netsh winsock reset proxy
net start bits
net start wuauserv
net start appidsvc
net start cryptsvc

Once done, restart the device and check.

 

If none will work from the above solution, I suggest doing an in-place upgrade, which will upgrade the device to the latest version and repair all issues without deleting any files.

 

Go to the Windows 11 website: https://www.microsoft.com/en-us/software-download/windows11

 

Under Download Windows 11 Disk Image (ISO), select Windows 11 (multi-edition ISO)

 

1.    Once done downloading the ISO, kindly right-click on the ISO, then click Mount> click Setup.exe

2.    You may be prompted by User Account Control. Click on Yes if so

3.    In the Install Windows 11 dialog, click Next

4.    Setup will check your PC and show a license agreement. Click on Accept in the license terms dialog.

5.    Wait for the setup program to check for the available free space.

6.    On the Ready to install page, make sure Keep personal files and apps have been checked.

7.    Then click Install and just follow the prompt.

8.    Windows 11 will restart your device several times and lead you to the lock screen. Depending on the options you set, it will keep all your files, apps, and user accounts.

Note: This is a public forum. I may respond shortly, but I apologize in advance for any delays. I am simply a fellow user trying to provide helpful insights and information.

Answer 2

Clear the Windows Update CacheCorrupted temporary files can cause hangs.Open Command Prompt as Administrator.Run these commands one by one to stop services:net stop wuauservnet stop bitsnet stop cryptsvcDelete all files in: C:\Windows\SoftwareDistribution\Download.Restart the services:net start wuauservnet start bitsnet start cryptsvc2. Run the .NET Framework Repair ToolSince this is a .NET-specific update, use Microsoft's dedicated tool to fix environment issues that general DISM scans might miss.Download and run the Microsoft .NET Framework Repair Tool.3. Perform a "Clean Component Cleanup"Run this specific DISM command to clear out superseded components that might be blocking the new update:dism /online /cleanup-image /startcomponentcleanup.Restart your PC and try the update again.4. Increase Trusted Installer Timeout (Advanced)If the install is timing out on your hardware, you may need to check your CBS.log for "CBS_E_HANG_DETECTED". In persistent cases, an In-place Upgrade (running the Windows 11 installation media over your current setup while keeping files) is the most reliable way to reset the servicing stack.