I have created a library project in
Add -> Existing Project
Add Reference ...
Unable to add a reference to project 'Xamarin.FormsBook.Toolkit'. The
targets of Portable Library project 'Xamarin.FormsBook.Toolkit' are
not the same or compatible with the targets of the current Portable
In Visual Studio 2017, Silverlight has been removed as an option.
You can edit the .csproj file of your FormsBook.Toolkit library and look for the Tag
<TargetFrameworkProfile>. To disable Silverlight, you should change it to
Profile111 (or the same thing your other library has).
You can find a list of these profiles in Stephen Cleary's Blog.