title: Nuget misbehaving with newtonsoft.json package
body: <p>Why Nuget producing an error when I install a package after <code>Newtonsoft.Json v11.0.2</code> is installed. Whenever I try to install another package I get the following error</p>
  
  <pre><code>Install-Package : An error occurred while retrieving package metadata for 'Newtonsoft.Json.11.0.2' 
  from source 'C:\Users\yusuf\Documents\Visual Studio 2015\Projects\Eman\packages'.
  At line:1 char:1
  + Install-Package MaterialDesignThemes
  + ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      + CategoryInfo          : NotSpecified: (:) [Install-Package], Exception
      + FullyQualifiedErrorId : NuGetCmdletUnhandledException,NuGet.PackageManagement.PowerShellCmdlets. 
     InstallPackageCommand
  </code></pre>
  
  <p>Whenever i remove the line with the Newtonsoft.json package defined in <code>packages.config</code> the package installs successfully. Is it something wrong with json package itself or is it my package manager that's messed up, anyway can someone show me how i can fix this.</p>
  
  <p><strong>P.S.</strong> This happens with whichever package i try to install while json package is already installed.</p>
  
  <p><strong>EDIT</strong> I tried deleting the package line in <code>packages.config</code> and also deleting the downloaded package files and reinstalled the package several times, i keep getting the same problem</p>