This has been asked many times before. The solution (which works for me) is to delete the *** package(s) from the packages.config file (this is enough), and from the package
I had the same issue with my visual studio 2015.
But Uninstalling the Nuget Package Manager and re-installing the same worked for me.
In Visual Studio, from the "Tools" menu choose the "Extensions and Updates" option. Top right "Search Installed" bar, sear ch for Nuget Package Manager Uninstall the Nuget Package Manager for Visual Studio 2015. Restart Visual Studio. Re-Install the same with the same steps.
close the visual studio and again open