'type': base type or interface is not CLS-compliant
A base type was marked as not having to be compliant with the Common Language Subset (CLS) in a module that was marked as being CLS compliant. Either remove the attribute that specifies the module is CLS compliant or remove the attribute that indicates the type is not CLS compliant.
The following sample generates CS3009:
using System; [assembly:CLSCompliant(true)] [CLSCompliant(false)] public interface I { void mf(); } public class C : I { // CS3009 public void mf () { } public static void Main () { } }