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

    LBR$_ILLCTL        Specified library control index not valid.
    LBR$_ILLIDXNUM     Library index number specified not valid.
    LBR$_LIBNOTOPN     Specified library not open.