title: Cannot add features to an Azure 2012 R2 VM
body: <p>I am trying to install .Net 3.5 through Roles &amp; Features. The message appears:</p>
  
  <blockquote>
    <p>Do you need to specify an alternate source path? One or more
    installation selections are missing source files on the destination
    server. The server will try to get missing source files from Windows
    Update, or from a location that is specified by Group Policy. You can
    also click the “Specify an alternate source path” link on this page to
    provide a valid location for the source files.</p>
  </blockquote>
  
  <p>I selected Install and it failed complaining it could not find the files.</p>
  
  <p>The VM is "Windows Server 2012 R2 Datacenter" from the Gallery</p>
  
  <p>Where are the source files? Have I missed something obvious?</p>