MIDL2187
The documentation lists this name without a value.
Documented in Win32
parameter must have either [in], [out] or [in,out] in this mode. You must specify /ms_ext or /c_ext The DCE IDL compiler requires all parameters to have explicit directional parameters. To use the Microsoft extensions to DCE IDL, you cannot use the /osf switch, which overrides /ms_ext and /c_ext .