title: I reverted back to MVC4, but now I can't build to a build server
body: <p>I am using VS 2012 and TFS 2010.
  Recently I failed to upgrade my application from MVC4 to MVC5.
  In order to do that I had to reassign the projects in my application to .Net Framework 4.5.
  The application worked on my development machine, but I could not get it to build to the build server.
  So in TFS version control I reverted back to the MVC4 version using .Net Framework 4.0.</p>
  
  <p>Now I find when I try to build to the build server, it fails.
  The error messages show that it is trying to build code that I had written for the MVC5 version.
  Yet that code no longer exists in my application.
  So I do not know why this is happening and how to fix it.</p>