Error: ASP.NET 4.0 has not been registered on the Web Server. You need to manually configure your Web Server for ASP.NET 4.0 in order for your site to run correctly.
Description: I experienced this error while trying to run a web site after upgrading the .NET framework to version 4.0 from version 3.5. This error occurs when we install IIS after .NET Framework installations because of that the .NET Framework was not properly registered or configured over IIS so the web sites can point to correct versions.
Solution: Multiple ways are there, Uninstall VS2010 and IIS then reinstall IIS followed by VS2010. Or, before doing reinstall try to register .NET Framework 4.0 with IIS7x by opening the Visual Studio Command Prompt (2010) under Administrative privileges, and then open framework folder “C:\Windows\Microsoft.NET\Framework\v4.0.30319“, enter aspnet_regiis -i to register .NET Framework 4.0 with IIS7x. If that not works, reinstall IIS, VS2010 and then register.