Looking at the response you got at SO, and your comment it look like neither of your projects is intended to be executable - so why are you producing an EXE file that cannot be executed? If you are producing Class libraries (as it suggests) then you should be producing .DLL files instead.
After that, I assume that you are trying to build your projects by pressing F5 - which tries to execute the Startup Project - which in you case is neither of these two projects.
Either:
1) Add a static Main method which reports a problem and exits:
[STAThread]
static void Main() { Console.WriteLine("This program is not executable"); }
Or
2) Add an executable program project to your solution and set it as the Startup project.
Myself, I'd go with the second option and use it as a "testbed" to test the other two projects...
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