The value for the 'compilerVersion' attribute in the provider options must be 'v4.0' or later if you are compiling for version ...

The value for the 'compilerVersion' attribute in the provider options must be 'v4.0' or later if you are compiling for version 4.0 or later of the .NET Framework. To compile this Web application for version 3.5 or earlier of the .NET Framework, remove the '{0}' attribute from the  element of the Web.config file.