MSKLC is asking for .NET Framework 3.5, not a newer 4.x version. A registry check showing a later .NET Framework version does not satisfy an app that specifically requires 3.5.
Since the repair tool was already tried, the next steps are:
- Open Windows Features and verify that .NET Framework 3.5 (includes .NET 2.0 and 3.0) is enabled.
- If it is already enabled, turn it off, restart Windows, then turn it on again.
- If Windows cannot enable it and shows errors such as 0x800F0906 or 0x800F081F, the source files are missing or Windows cannot download them.
- In that case, allow Windows to contact Windows Update directly to download repair content, or provide a valid local source path for the .NET 3.5 files.
- If the .NET Framework installation itself is corrupted, run the Microsoft .NET Framework Repair Tool again. It supports repairing .NET Framework 3.5 SP1 and newer supported versions.
If the issue is during a build or targeting step rather than Windows feature installation, the related MSBuild error is MSB3645, which indicates that .NET Framework v3.5 Service Pack 1 was not found. The documented resolution is to install that framework version or target a newer framework if the application supports it.
References: