SQL & PL/SQL

Hello,i am on 10.2.0.3.0 and i have problems when i try to use materialize hint.
If i go with this query :

WITH a AS
     (SELECT 
             ca.customer_id_high, ca.customer_id,
             NVL (ca.cscomptaxno, ca.passportno) jmbg
        FROM customer_all@vipbscs ca
       WHERE ca.cstype <> 'd'),
     b AS
     (SELECT 
             co.customer_id, co.co_id contract_id,
             cis.billing.cotomsisdn (co.co_id) msisdn
        FROM contract_all@vipbscs co),
     c AS
     (SELECT pah.cid
        FROM pa_head_agent pah, pa_teams t, pa_team_agents ta
       WHERE pah.agent_id = ta.agent_id
         AND t.ID = ta.team_id
         AND t.ID IN (21)
         AND ta.agent_id IN (10210))
SELECT     b.contract_id, b.msisdn, a.customer_id, a.jmbg, ka.nr ka_nr
      FROM a, b, ka_head ka
     WHERE a.customer_id = ka.cid(+) AND a.customer_id = b.customer_id(+)
CONNECT BY PRIOR a.customer_id = a.customer_id_high
START WITH a.customer_id IN (SELECT cid
                               FROM c)

It takes years to finish.

And if i go with this query, exeplain plan is showing let's say exceptable execution time estimation, but it fails with ORA-12840: cannot access a remote table after parallel/insert direct load txn :

WITH a AS
     (SELECT /*+ MATERIALIZE */
             ca.customer_id_high, ca.customer_id,
             NVL (ca.cscomptaxno, ca.passportno) jmbg
        FROM customer_all@vipbscs ca
       WHERE ca.cstype <> 'd'),
     b AS
     (SELECT /*+ MATERIALIZE */
             co.customer_id, co.co_id contract_id,
             cis.billing.cotomsisdn (co.co_id) msisdn
        FROM contract_all@vipbscs co),
     c AS
     (SELECT pah.cid
        FROM pa_head_agent pah, pa_teams t, pa_team_agents ta
       WHERE pah.agent_id = ta.agent_id
         AND t.ID = ta.team_id
         AND t.ID IN (21)
         AND ta.agent_id IN (10210))
SELECT     b.contract_id, b.msisdn, a.customer_id, a.jmbg, ka.nr ka_nr
      FROM a, b, ka_head ka
     WHERE a.customer_id = ka.cid(+) AND a.customer_id = b.customer_id(+)
CONNECT BY PRIOR a.customer_id = a.customer_id_high
START WITH a.customer_id IN (SELECT cid
                               FROM c)

Can you suggest something i could do optimize this query ?
I can post explan plan if you thing it could help.