When I attempt to add a reference to a class library type project within the same solution, I get a message box saying:
A reference to 'YourProject' could not be added. An assembly must have a 'dll' or 'exe' extension in order to be referenced.
I am using Visual Studio Community Edition 2015 on 64-bit Windows 7 Home Premium and all my projects, the one I am trying to set a reference to as well as the one I am trying to set a reference from target .NET Framework v4.