COM interface and .NET interoperability

VC++ COM interface in a DLL : ------------------------------- interface IModuleConfig { HRESULT SetValue( const GUID* pParamID, VARIANT* pValue); }; DLL component Id is 9C9A2859-C76B-4205-A52A-3ADBA54458B7. DLL component implements this interface...   C# code : I created the instance for the DLL component as follows : [ ComImport, Guid ("9C9A2859-C76B-4205-A52A-3ADBA54458B7")] public class DLLComponent { }   This is like defining the CLSID in VC++...   How to create an instance for the specified Guid ?   Type t = typeof(DLLComponent); DLLComponent dllComponent; dllComponent = Activator.CreateInstance(t);     How to Query the interface from the DLL component Instance ? IModuleConfig config = null; config = dllComponent as IModuleConfig; or config = (IModuleConfig) dllComponent; But we have to declare the IModuleConfig interface in the C# as follows ; [ ComImport, System.Security.SuppressUnmanagedCodeSecurity , Guid("486F726E-4D43-49b9-8A0C-C22A2B0524E8" ), InterfaceType(ComInterfaceType .InterfaceIsIUnknown)] public interface IModuleConfig { [PreserveSig] int SetValue([In , MarshalAs(UnmanagedType .LPStruct)]Guid guid, ref Object obj); } Afterwards we can call the interface method using its object with dot operator... IModuleConfig config = null; config = dllComponent as IModuleConfig; config.SetValue(guid, ref obj);   Now it is working well. Wrong code: ============== Previously I defined the C# interface as follows : [ ComImport, System.Security.SuppressUnmanagedCodeSecurity , Guid("486F726E-4D43-49b9-8A0C-C22A2B0524E8" ), InterfaceType(ComInterfaceType .InterfaceIsIUnknown)] public interface IModuleConfig { [PreserveSig] int SetValue([In , MarshalAs(UnmanagedType .LPStruct)]Guid guid,[In , MarshalAs(UnmanagedType .AsAny) ref Object obj); } I got the exception as follows, we can't use the "UnmanagedType .AsAny" ref types and Array with offset parameters.   I thank verymuch to muthu pandi anna for helping me to solve this problem.   For VARIANT* we have to use the ref type.