title: Missing type Microsoft.CSharp.RuntimeBinder.Binder
body: <p>My project won't build because of the following error: </p>
  
  <blockquote>
    <p>Predefined type 'Microsoft.CSharp.RuntimeBinder.Binder' is not defined or imported.</p>
  </blockquote>
  
  <p>What reference do I need to add?</p>