VMS Help CC, Messages, UNKNOWNMACRO  *Conan The Librarian (sorry for the slow response - running on an old VAX)

 Message        "<name>" is not currently defined as a macro.  It has
                been replaced by the constant zero.

 Description    An identifier found in an #if or #elif is not
                defined.  This might not have been what you intended.
                The compiler will replace the identifier with the
                constant zero.

 User Action    Verify the use of the identifier.