As I have mentioned earlier in my last blog post, .NET 3.5 SP1 first had the concept called Profiles. In .NET 3.5 SP1 it was possible to build an app for Client Profile. The idea is to create subset of the whole .NET Framework, which is very big for easier install, maintenance and less memory footprint. Since Client Apps really need a subset of whole .NET Framework, .NET 3.5 Client Profile contains only client specific libraries like ASP.NET, WPF, CLR and WinForms. Libraries like ASP.NET or LINQ were not included as they are not required for Client Apps.
Now in .NET 4, there is one more profile available – called Server Core Profile. Server Core Profile is a subset of the .NET framework for server applications. It can run server oriented applications like ASP.NET and WCF.
As you can guess, Server Core profile does not contain Client UI specific libraries like WPF and WinForms. So if you create a WPF or WinForms app and change the Target Framework (in Project properties dialog) to .NET Framework 3.5 Server Profile, certain dlls (from WPF or WinForms) would be missing and you would get an error while compiling the app.
Now as you can see, there isn’t a Server profile available for .NET Framework 4 in Beta 2. You can expect to see that when .NET 4 (and VS 2010) is finally released by Microsoft this year.