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Compiler Warning (level 1) CS3009 

Error Message

'type': base type 'type' is not CLS-compliant

A base type was marked as not having to be compliant with the Common Language Specification (CLS) in an assembly that was marked as being CLS compliant. Either remove the attribute that specifies the assembly is CLS compliant or remove the attribute that indicates the type is not CLS compliant. For more information on CLS Compliance, see Writing CLS-Compliant Code and Common Language Specification.


The following example generates CS3009:

// CS3009.cs

using System;

public class B

public class C : B   // CS3009
    public static void Main () {}