Nuget Package Restore
When opening your YetaWF Visual Studio solution for the first time and building all projects, make sure that the Nuget Package Manager is set to automatically download missing packages. We don't distribute third-party packages that are available via Nuget so they need to be downloaded when you build the solution the first time.
You can enable automatic package restore using the Visual Studio menu Tools > Nuget Package Manager > Package Manager Settings. Make sure to enable both check boxes: