Oracle - Error suma de variables

declare

v_norder NUMBER(5) ;

SCLIENT char(14);

begin

v_norder:=0;

SCLIENT :='12050946';

dbms_output.put_line ('SCLIENT  Inicia en: '|| SCLIENT);

dbms_output.put_line ('v_norder Inicia en: '|| v_norder);

select (to_number(max(nvl(fono.norder,0))) + 1)

        into v_norder

        from address dir

        inner join phones fono on dir.skeyaddress = fono.skeyaddress

        where dir.sclient = lpad(SCLIENT,14,'0');

dbms_output.put_line ('V_NORDER FIN: '|| v_norder);

dbms_output.put_line ('CLIENTE: '||SCLIENT);

end;

(to_number(max(nvl(fono.norder,0))) + 1) into v_norder