Nuget Package ... does not exist in project ... Package ... Already exists in folder
Close the solution then go to the packages folder on your hard drive and delete all its contents. Open your application again in Visual Studio and it will automatically try to restore the packages. Clean the Solution and Build it.
Clearing the cache solved the problem for me. There's an option to clear the cache on Tools > Options > NuGet Package Manager > General menu, called Clear All NuGet Cache(s).
First, uninstall via package manager console the specific NuGet package
Then, please unload the project where this nugget package was referenced for by right click -> Unload Project.
After unloading right click in the project and select "Edit {Project Name}.csproj"
Find the NuGet package entry within the XML where you previously uninstalled and delete it.
Install again the package from package manager console...