ORA-01502: index is in unusable state

I am using sqlloader with direct=TRUE , i am trying to insert 2 million records in to table through flat files. This flat files some times may have duplicated records also.
(using Direct Path Load)

The loading tables has a primary key constraint on some columns.

Sqlloader is loading successfully but the index which is created for primary key by default by oracle
is getting in unusable state.

1>Due to this the select query in the procedure is giving the error that index is in unsable state.

ORA-01502: index 'DOS_OWNER.PK_MARKETING_COPY1234' or partition of such
index is in unusable state


2>I am not able to even delete the duplicate records also because for the same error.

SQL> alter session set skip_unusable_indexes=true;

Session altered.

SQL> ed
Wrote file afiedt.buf

  1  delete from marketing_copy
  2   where rowid in ( select rowid
  3     from ( select
  4   row_number() over ( partition by full_isbn,
  5  region,
  6  marketing_copy_type,load_date
  7   order by full_isbn ) rn
  8                          from marketing_copy )
  9*                        where rn <> 1)
SQL> /
delete from marketing_copy
*
ERROR at line 1:
ORA-01502: index 'GLOBAL_HEPM_OWNER.PK_MARKETING_COPY1234' or partition of such
index is in unusable state


3> I am not able to re build also
SQL> alter index PK_MARKETING_COPY1234 rebuild;
alter index PK_MARKETING_COPY1234 rebuild
*
ERROR at line 1:
ORA-01452: cannot CREATE UNIQUE INDEX; duplicate keys found
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I am using
Oracle9i Enterprise Edition Release 9.2.0.1.0 - Production
With the Partitioning, OLAP and Oracle Data Mining options
JServer Release 9.2.0.1.0 - Production


1) How to proceed now any logic/method to handle this situation.
2) how can i rebuild my index / How delete duplicate records

Please Help me ouT....!