title: Error when trying to install any package from NuGet
body: <p>I'm getting a message like this when trying to install a package using NuGet:  </p>
  
  <p><code>
  Install-Package : Unable to find package 'Newtonsoft.Json'.
  At line:1 char:16
  + Install-Package &lt;&lt;&lt;&lt;  Newtonsoft.Json
      + CategoryInfo          : NotSpecified: (:) [Install-Package], InvalidOperationException
      + FullyQualifiedErrorId : NuGetCmdletUnhandledException,NuGet.PowerShell.Commands.InstallPackageCommand
  </code></p>
  
  <p>(the same error for other packages). Tried to reinstall NuGet - no success.<br>
  Any other ideas?</p>