title: The type 'System.IDisposable' is defined in an assembly that is not referenced
body: <p>I created a Windows Form application in Visual Studio 2012 on Windows 8, and the target .NET framework is 4.5, and I want to use the Datagramsocket library of Windows SDK, so I changed the target OS version to 8, when I compile. </p>
  
  <p>I am getting the following error:</p>
  
  <blockquote>
    <p>"Error 1   The type 'System.IDisposable' is defined in an assembly that is not referenced. You must add a reference to assembly 'System.Runtime, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a'."</p>
  </blockquote>