title: InternalsVisibleTo causes CS0246 error: The Type or Namespace could not be found
body: <p>I am trying to enable one assembly to access another assembly's internal classes by adding</p>
  
  <pre><code>[assembly:InternalsVisibleTo("assembly-name")]
  </code></pre>
  
  <p>to the second assembly.  However, this causes the following error:</p>
  
  <pre><code>error CS0246: The type or namespace name 'InternalsVisibleTo' could not be found (are you missing a using directive or an assembly reference?)
  </code></pre>
  
  <p>I am following the examples here:
  <a href="http://msdn.microsoft.com/en-us/library/0tke9fxk.aspx" rel="nofollow noreferrer">MSDN Reference</a></p>
  
  <p>What am I doing wrong?</p>