I am converting a Silverlight application to use C#/XAML for HTML5. The original solution contains the project and 4 Class Library projects. One of the class library projects is not compiling on a HashSet with the error:
The type 'System.Collections.Generic.ISet`1<T0>' is defined in an assembly that is not referenced. You must add a reference to assembly 'System, Version=18.104.22.168, Culture=neutral, PublicKeyToken=b77a5c561934e089'.
Where do I find this reference? When I add System.dll, it tells me to remove it.