query which returns 2 or more results

O have this error
Invalid identifier: CH.CH_REASON reason_id,

SELECT /*+DRIVING_SITE(ch)*/ /*+DRIVING_SITE(co)*/ /*+DRIVING_SITE(cu)*/ /*+DRIVING_SITE(cc)*/ /*+DRIVING_SITE(rp)*/ /*+DRIVING_SITE(icc)*/ /*+DRIVING_SITE(dt)*/
 dt.dn_num NRO_TELEFONO,
 dt.co_id,
 ch.ch_validfrom FECHA_ACUERDO,
 dt.customer_id,
 cu.custcode,
 cu.cscompregno RUC_DNI,
 cc.ccname RAZON_SOCIAL,
 cc.ccaddr1 || ' ' || cc.ccaddr3 || ' ' || cc.ccstreet || ' ' || cc.cccity DIRECCION,
 cu.prgcode TIPO_CLIENTE,
 dt.tmcode CODIGO_PLAN,
 decode(substr(rp.shdes, 0, 3), 'CON', 'C', 'P') TIPO_PLAN,
 'A' ESTADO_LINEA,
 --F_OBTENER_CF(dt.tmcode) CARGO_FIJO,
 --F_OBTENER_DEVIATING(dt.co_id, dt.tmcode) DEVIATING,
 decode(cu.cscusttype,
        'C',
        nvl(icc.combo14, icc.combo06),
        'B',
        nvl(icc.combo06, icc.combo14),
        'LIBRE') ACUERDO,
 CH.CH_REASON reason_id,
 (SELECT A.RS_DESC
    FROM SYSADM.REASONSTATUS_ALL A
   WHERE A.RS_ID = CH_REASON) REASON_DES,
 '0' FLAG_PROCESADO,
 TIM.TFUN105_TIPO_PRODUCTO(dt.dn_num) TIPO_PRODUCTO
  FROM SYSADM.contract_all     co,
       SYSADM.customer_all     cu,
       SYSADM.ccontact_all     cc,
       SYSADM.rateplan         rp,
       SYSADM.info_contr_combo icc,
       tim.pp_datos_contrato   dt,
       (select chi.co_id,max(chi.ch_validfrom) ch_validfrom SYSADM.contract_history  chi where chi.ch_seqno = 2 group by chi.co_id )ch
 WHERE cu.prgcode in (2)  
   AND ch.co_id = co.co_id
   AND co.customer_id = cu.customer_id
   AND co.customer_id = cc.customer_id
   AND co.tmcode = rp.tmcode
   AND co.co_id = icc.co_id
   AND cc.ccbill = 'X'
   AND co.customer_id = dt.customer_id
   AND co.co_id = dt.co_id
--   AND (ch.ch_validfrom BETWEEN TO_DATE('20101115', 'YYYYMMDDhh24miss') AND TO_DATE('20101118', 'YYYYMMDDhh24miss'))
--   AND ch.ch_validfrom > TO_DATE('20101115', 'YYYYMMDDhh24miss') --fecha desde
   AND ch.ch_validfrom < TO_DATE('20101115', 'YYYYMMDDhh24miss') --fecha hasta
   AND  dt.dn_num in (997351247)

I have the same results

SELECT /*+DRIVING_SITE(ch)*/ /*+DRIVING_SITE(co)*/ /*+DRIVING_SITE(cu)*/ /*+DRIVING_SITE(cc)*/ /*+DRIVING_SITE(rp)*/ /*+DRIVING_SITE(icc)*/ /*+DRIVING_SITE(dt)*/
 dt.dn_num NRO_TELEFONO,
 dt.co_id,
 ch.ch_validfrom FECHA_ACUERDO,
 dt.customer_id,
 cu.custcode,
 cu.cscompregno RUC_DNI,
 cc.ccname RAZON_SOCIAL,
 cc.ccaddr1 || ' ' || cc.ccaddr3 || ' ' || cc.ccstreet || ' ' || cc.cccity DIRECCION,
 cu.prgcode TIPO_CLIENTE,
 dt.tmcode CODIGO_PLAN,
 decode(substr(rp.shdes, 0, 3), 'CON', 'C', 'P') TIPO_PLAN,
 'A' ESTADO_LINEA,
 --F_OBTENER_CF(dt.tmcode) CARGO_FIJO,
 --F_OBTENER_DEVIATING(dt.co_id, dt.tmcode) DEVIATING,
 decode(cu.cscusttype,
        'C',
        nvl(icc.combo14, icc.combo06),
        'B',
        nvl(icc.combo06, icc.combo14),
        'LIBRE') ACUERDO,
 CH.CH_REASON reason_id,
 (SELECT A.RS_DESC
    FROM SYSADM.REASONSTATUS_ALL A
   WHERE A.RS_ID = CH_REASON) REASON_DES,
 '0' FLAG_PROCESADO,
 TIM.TFUN105_TIPO_PRODUCTO(dt.dn_num) TIPO_PRODUCTO
  FROM SYSADM.contract_all     co,
       SYSADM.customer_all     cu,
       SYSADM.ccontact_all     cc,
       SYSADM.rateplan         rp,
       SYSADM.info_contr_combo icc,
       tim.pp_datos_contrato   dt,
       (select CH_REASON,chi.co_id,max(chi.ch_validfrom) ch_validfrom
        from SYSADM.contract_history  chi
        where chi.ch_seqno = 2 group by CH_REASON,chi.co_id ) ch
 WHERE cu.prgcode in (2)  
   AND ch.co_id = co.co_id
   AND co.customer_id = cu.customer_id
   AND co.customer_id = cc.customer_id
   AND co.tmcode = rp.tmcode
   AND co.co_id = icc.co_id
   AND cc.ccbill = 'X'
   AND co.customer_id = dt.customer_id
   AND co.co_id = dt.co_id
--   AND (ch.ch_validfrom BETWEEN TO_DATE('20101115', 'YYYYMMDDhh24miss') AND TO_DATE('20101118', 'YYYYMMDDhh24miss'))
--   AND ch.ch_validfrom > TO_DATE('20101115', 'YYYYMMDDhh24miss') --fecha desde
   AND ch.ch_validfrom < TO_DATE('20101115', 'YYYYMMDDhh24miss') --fecha hasta
   AND  dt.dn_num in (997351247)

query which returns 2 or more results, can help me modify it to return the largest fecha_acuerdo

...
(select CH_REASON,chi.co_id, ch_validfrom,
       ,row_number() over (partition by chi.co_id order by ch_validfrom desc) rn
        from SYSADM.contract_history  chi
        where chi.ch_seqno = 2) ch
where ...
and ch.rn = 1

and modify the query but I have the same results
 
SELECT
 dt.dn_num NRO_TELEFONO,
 dt.co_id,
 ch.ch_validfrom FECHA_ACUERDO,
 TIM.TFUN105_TIPO_PRODUCTO(dt.dn_num) TIPO_PRODUCTO
  FROM SYSADM.contract_all     co,
       SYSADM.customer_all     cu,
       SYSADM.ccontact_all     cc,
       SYSADM.rateplan         rp,
       SYSADM.info_contr_combo icc,
       tim.pp_datos_contrato   dt,
        (select CH_REASON,chi.co_id,ch_validfrom,
                ROW_NUMBER() OVER (PARTITION BY chi.co_id ORDER BY ch_validfrom DESC) RN
        from SYSADM.contract_history  chi
        where chi.ch_seqno = 2) ch
 WHERE cu.prgcode in (2)  
   AND ch.co_id = co.co_id
   AND co.customer_id = cu.customer_id
   AND co.customer_id = cc.customer_id
   AND co.tmcode = rp.tmcode
   AND co.co_id = icc.co_id
   AND cc.ccbill = 'X'
   AND co.customer_id = dt.customer_id
   AND co.co_id = dt.co_id
   AND CH.RN = 1
   AND ch.ch_validfrom < TO_DATE('20101115', 'YYYYMMDDhh24miss') --fecha hasta
   AND  dt.dn_num in (997351247)
   and ch.rn = 1

Please experts, I made the changes suggested and still does not work, please appreciate their support

I execute the query but i have This error
Ora - 01114

This:
select * from
(select CH_REASON,chi.co_id,ch_validfrom,
                ROW_NUMBER() OVER (PARTITION BY chi.co_id ORDER BY ch_validfrom DESC) RN
        from SYSADM.contract_history  chi
        where chi.ch_seqno = 2)
where rn = 1;

Hi Experts
This query

 a mi yahoo por favor: enrique_aeo@yahoo.com
 
select V_DN_NUM,
       N_CO_ID,
       D_CH_VALIDFROM,
       N_CUSTOMER_ID,
       V_CUSTCODE,
       V_CSCOMPREGNO,
       V_CCNAME,
       V_DIRECCION,
       V_PRGCODE,
       N_TMCODE,
       V_TIPO_PLAN,
       V_ACUERDO,
       N_CH_REASON,
       V_REASON_DES,
       D_FECHA_CARGA,
       V_DESC_TIPO_OPERACION
  from sigat_activaciones_tmp act
 where act.v_dn_num in 997351247

I need This Max valué     D_CH_VALIDFROM

Thank you all for your help. I resolved the problem in 2 parts. First find the maximum date and store it in a variable. Then use that variable in my query