VMS Help SMB Routines, SMB$READ_MESSAGE, Condition Values Returned  *Conan The Librarian (sorry for the slow response - running on an old VAX)

    SS$_NORMAL         Normal successful completion.
    LIB$_INVARG        Routine completed unsuccessfully because of an
                       invalid argument.

    This routine also returns any of the condition codes returned by
    the Run-Time Library string-handling (STR$) routines.