Links between .NET Framework versions
No, this is not possible, but not because of the difference in structure. This is not possible because your client does not have the assemblies required for WCF.
Actually, .NET 2.0 and .NET 3.5 use the same CLR. If you are compiling code for .NET 3.5, but are not using any of the new assemblies, then it should be possible for that code to use a .NET 2.0 application..NET 3.5 is just .NET 2.0 SP2 plus a few new assemblies.
In fact, .NET 3.0 is .NET 2.0 SP1 plus a few new assemblies .. NET 3.5 is .NET 2.0 SP2 plus .NET 3.0 SP1 plus new assemblies. All three use CLR.NET 2.0.
.NET 4.0 uses the new CLR and is a new version. .NET 4.0 code cannot run on a .NET 2.0 machine. However, there is a feature that allows the CLR to run .NET 2.0 and .NET 4.0 at the same time.
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