title: Build error: You must add a reference to System.Runtime
body: <p>I'm preparing a brand new ASP.NET MVC 5.1 solution. I'm adding in a bunch of NuGet packages and setting it up with Zurb Foundation, etc.</p>
  <p>As part of that, I've added a reference to an in-house NuGet package which is a Portable Class Library and I think this is causing a problem on the build server.</p>
  <p>TeamCity fails the build with:</p>
  <blockquote>
  <p>The type 'System.Object' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime, Version=4.0.0.0</p>
  </blockquote>
  <p>I originally added the fix for the same or similar error when compiling the Razor web pages, that fix being in the <code>web.config</code></p>
  <pre class="lang-xml prettyprint-override"><code>&lt;compilation ... &gt;
    &lt;assemblies&gt;
      &lt;add assembly=&quot;System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a&quot; /&gt;
    &lt;/assemblies&gt;
  &lt;/compilation&gt;
  </code></pre>
  <p>However, the issue is unresolved.</p>