.NET Framework Errors After Windows 10 Update - Files Missing

I have a problem that started after a Windows Update that I have not been able to resolve despite all my research and my many attempts to uninstall/re-install updates, recover restore points, and repair .NET framework. I’m hoping someone here can help.

This computer uses Windows 10 Home 1903. Home has limited control of updates. .NET Framework is integrated, i.e. it can’t be uninstalled (NOTE: I am NOT using this computer for development work).

On 6/22, two updates were applied - KB4560960 (2020-06 Cumulative Update for Windows 10 Version 1903) and KB4561600 (Adobe Flash Player Security Update) – and the computer rebooted. Two error boxes appeared, the first one was titled “Update.exe - .NET Framework Initialization Error” with the text “To run this application, you first must install one of the following versions of the .NET Framework: v4.0.30319 Contact your application publisher for instructions about obtaining the appropriate version of the .NET Framework.” After a moment, the second one appeared titled “IAStorIcon.exe” with the same text but referencing v4.0.

The Update.exe box was tied to the Microsoft Teams icon on the task bar – but I have never installed Microsoft Teams and the updates did not include that application.

Tried to go back to the restore point created just prior to the offending updates (KB4560960 and KB4561600) but after running for 6 hours, it failed saying it couldn’t replace a Firefox file in AppData. Tried many things to resolve the restore problem but nothing worked. Ran chkdsk and sfc which did not find any problems.

Since the errors are both related to .NET, I focused on resolving .NET issues. I noticed that on 6/8, update KB4552931 (Cumulative Update for .NET Framework 3.5 and 4.8) failed to install with error code 0x80240017. I uninstalled this update, rebooted and got the same 2 error boxes. I downloaded KB4552931 from Microsoft’s site, ran it, rebooted, errors continued.

I installed .NET Framework 4.8 using ndp48-web.exe from the Microsoft website. It said “.NET Framework 4.8 or a later update is already installed on this computer”. The errors are complaining about .NET 4.0x, so I tried to install .NET 4.0 but as exepected, got “Microsoft .NET Framework 4 is already a part of this operating system” and the “Same or higher version of .NET Framework 4 has already been installed”. Since .NET does not appear in Programs and Features, I went to “Turn Windows features on or off” and checked boxes “.NET Environment”, “.NET Extensibility 3.5”, “.NET Extensibility 4.8” and “ASP.NET 4.8” and hit Close – it said it was done making changes. When I re-opened the features dialog, the boxes I checked were no longer checked. I rebooted and the same 2 error boxes appeared.

Looked on web for .NET repair possibilities. Microsoft has a repair tool, clean up tool and verification tool but they only go up to 4.7. I ran the repair and clean up tools which had no effect (.NET Framework Repair Tool: https://www.microsoft.com/en-us/download/details.aspx?id=30135, .NET Clean Up Tool: https://docs.microsoft.com/en-us/archive/blogs/astebner/net-framework-cleanup-tool-users-guide)

The .NET Framework Verification Tool (netfx_setupverifier.exe from https://docs.microsoft.com/en-us/archive/blogs/astebner/net-framework-setup-verification-tool-users-guide) allows you to select the version you want to verify – the dropdown only listed versions 2.0, 3.0, and 3.5.

Saw an article on how to determine .NET versions and what is in the registry (https://docs.microsoft.com/en-us/dotnet/framework/migration-guide/how-to-determine-which-versions-are-installed). The article showed the image below but my registry only showed the (Default) entry.

I verified that the path referenced in InstallPath existed on my drive. I added all of the entries shown above into my registry. The Release and Version actually reference the November 2019 update but it’s the May 2020 one that is installed and causing trouble. I uninstalled that update again and reinstalled it – it did not make any changes to the registry and the errors continued. The verification tool (netfx_setupverifier.exe), however, now showed versions 2.0, 3.0, 3.5, and every version of 4.x up to 4.7 in the dropdown. Ran this for 4.7 and 4 Full which both failed. The log file said that many files were missing from C:\Windows\Microsoft.NET\Framework64\v4.0.30319 and C:\WINDOWS\Microsoft.NET\assembly. I found another Windows 10 Home computer and compared the files in C:\Windows\Microsoft.NET\Framework64\v4.0.30319 – I have very few files in my folder compared to the "good" computer:

So my registry was missing 4.0 information until I manually added it but many files on the drive are also missing. Everything was fine until the 6/22 update (I also tried uninstalling the updates to no avail, I am limited in which updates I can undo).