MIDL2252
The documentation lists this name without a value.
Documented in Win32
use of an unknown type for [represent_as] or [user_marshal] not supported for /Oi modes, using /Os Use of the [ represent_as ] attribute with a local type that is not defined in the IDL file or an imported IDL file can be handled only by /Os optimization stubs. The stubs for this routine will be generated using /Os optimization.