This started happening with 6.0.4 recently for me, I don't think this is a very good solution but here is what helped me.
Close Visual Studio
- Open a Windows PowerShell prompt as Administrator (very important) and run the following command:Set-ExecutionPolicy Bypass
- Open Visual Studio, open your solution and use Nuget to install JSON.Net (or whatever package included it as a dependency).
- Once everything is working, I recommend setting the powershell execution policy back to restricted with the following command:
Set-ExecutionPolicy Restricted