When you compile a .NET 4.0 C# application the following error message appears: The type or namespace name … could not be found (are you missing a using directive or an assembly reference?) There is also a warning message : The currently targeted framework “.NET Framework,Version=v4.0,Profile=Client” does not include “System.Web, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a” which the …