title: Install-Package : Failed to add reference to 'System.Runtime'
body: <p>I'm trying to install the Autofac nuget package in my project using the command</p>
  
  <pre><code>Install-Package -Prerelease Autofac
  </code></pre>
  
  <p>but it fails with the error</p>
  
  <pre><code>Install-Package : Failed to add reference to 'System.Runtime'. Please make sure that it is in the Global Assembly Cache.
  </code></pre>
  
  <p>I've tried re-installing .NET Framework 4.5.2 (which is the version my project targets) but got the message ".NET Framework 4.5.2 is already installed". However, searching <code>C:\Windows\assembly\</code> for <code>System.Runtime.dll</code> doesn't find any exact matches (although there are a few instances of <code>System.Runtime.ni.dll</code>, which (seem to indicate) that they are really the same assembly...).</p>
  
  <p>What can I do about this?</p>
  
  <p><img src="https://i.stack.imgur.com/kAdvX.png" alt="project config"></p>
  
  <p><strong>Update:</strong> apparently I was confused about the location of the GAC. <a href="https://stackoverflow.com/users/47589/amy">Amy</a> enlightened me, and searching in <code>C:\Windows\Microsoft.NET\assembly</code> instead I <em>do</em> find <code>System.Runtime.dll</code>. Why doesn't Visual Studio?</p>