To identify and clean-up issues related to the installation of the Microsoft .NET Framework:
A link to the tools can be found here: .NET Framework setup verification tool and cleanup tools
• First use the validation tool to establish if there is a problem with .NET or not.
• If there is, first try running a repair via the Windows > Control Panel > Programs and Features.
• Use the validation tool to check if the problem was fixed.
• If not, use the cleanup tool.