 <p>When I try this: [MarshalAsAttribute(UnmanagedType.SafeArray, SafeArrayUserDefinedSubType = typeof(Inner))]</p> <p>I get: An unhandled exception of type 'System.ArgumentException' occurred in Driver.exe</p> <p>Additional information: The parameter is incorrect. (Exception from HRESULT: 0x80070057 (E_INVALIDARG))</p>