Nuget - Nuget adds broken References without path.

I did already try Update-Package -reinstall. But this did not help.
I also removed all references manually and empied the package folder without results.

The solution:
Clear the nuget cache (don't know if this was necessary). Under tools -> Nuget Package Manager -> Nuget Settings and Clear cache.

Unload proj from solution
Edit csproj file and delete nuggets entries from csproj file (ItemGroup).
Reload proj
It works!!