Referenced class 'class1' has unknown base class or interface 'class2'
A class that was imported from a file with /reference, is derived from a class or implements an interface that is not found. This could occur if a required .DLL is not also included in the compilation with /reference.
The following sequence of compilations will result in CS0011:
// B1.CS class B1 { public static void Main() { } }
Then:
// B2.CS; compile with /I:b1.exe class B2: B1 { public static void Main() { } }
Ignoring the CS0114 warning. Then:
// D.CS; compile with /I:b2.exe namespace B1 { class D1 { B2 b2; public static void Main() { } } }
You could resolve this CS0011 by compiling with /reference:b2.exe;b1.exe
and by changing the name of the namespace in d.sc so that it does not conflict with the class name in B1.CS.