Al final lo resolví de la siguiente manera
Código SQL
[-]
Select Cod_in
from mb999Indicadores IND, mb999RegMedicion RM
where IND.Cod_in = RM.Ind_rm
and IND.des_in = 0 and (RM.Fme_rm + IND.Per_in <= '06/01/2005')
and (cast(Ind_rm as char(4)) + cast(Fme_rm as char(10))) in
(Select (cast(Ind_rm as char(4)) + cast(max(Fme_rm) as char(10))) from mb999RegMedicion group by Ind_rm)