title: Visibility issues with Pex
body: <p>I tried to use generate unit tests for some parts of code in my project. But all I get is the same error everytime, and the messages offered are'nt very helpful to arrive at a solution. Pex says that the code is not visible to it. But if i add the required classes and their dependencies to another solution, it works fine. Has anyone else faced this issue and found an answer?</p>