In the section of the Web.config file, the value for the 'compilerVersion' attribute in the provider options must be 'v2.0' ...

In the  section of the Web.config file, the value for the 'compilerVersion' attribute in the provider options must be 'v2.0' if you are targeting version 2.0 or 3.0 of the .NET Framework, or must be 'v3.5' if you are targeting version 3.5 of the .NET Framework. If you are compiling this Web application for version 4.0 or later of the .NET Framework, the '{0}' attribute is required in the  element of the Web.config file instead (for example, '').