title: The type is defined in an assembly that is not referenced
body: <p>I've just begun incorporating a few projects from a partner office's solution into our solution.  The program is a C# winform application.</p>
  
  <p>The program compiled and everything was going fine, but then yesterday I went to build again and out of nowhere it threw an error <strong>"The type 'Namespace.MainFrameDisplay' is defined in an assembly that is not referenced.  You must add a reference to assembly 'OtherAssembly, Version=1.7.0.0, Culture=neutral, PublicKeyToken=52af1880d3cd7291"</strong>  (As far as I can tell, OtherAssembly isn't used as a reference in the original project. There are compatibility issues between Assembly and OtherAssembly, adding OtherAssembly nets about 100 errors.)</p>
  
  <p>As well as a related error <strong>"Cannot implicitly convert type 'Namespace.MainFrameDisplay' to 'Namespace.MainFrameDisplay'  [c:\Dev\program\bin\debug\Assembly.dll]</strong>  </p>
  
  <p>A snippet of psuedo-code for the error is:</p>
  
  <pre><code>private MainFrameDisplay _MainFrame;  //definition
  _MainFrame = this.Mainframe;  // error is thrown here
  _MainFrame.Parent.Controls.Add(_NotifyBar);
  </code></pre>
  
  <p>If I delete the definition, the error remains.<br>
  If I take out the line where the error is thrown, it compiles fine.  Even with calling the _MainFrame.Parent.</p>
  
  <p>I've gone so far as to delete/remove this troublesome project and unzip/add a new copy of the original, but the problem remains.  Any thoughts, suggestions?</p>