title: Visual Studio 2012 How to debug "Unable to add reference to project x" error?
body: <p>In Visual Studio 2012 in a blank new Class Library I am trying to add reference to an existing project in the solution, also a Class Library, MonoGame.Framework.Windows8 (<a href="https://github.com/mono/MonoGame" rel="noreferrer">https://github.com/mono/MonoGame</a>), but get the error:</p>
  
  <blockquote>
    <p>Unable to add reference to Project MonoGame.Framework.Windows8</p>
  </blockquote>
  
  <p>I have built the existing library, MonoGame, successfully and made it a dependency of the new one. What could be the problem?</p>
  
  <p>(It's extremely annoying the error message does not give a reason!)</p>