Duplicate primary key and also the OID !!!!

Hi all,
I'm running postgres 7.3.2 and in a table with a primary key
I got that primary key duplicated :-(

I found this because each time that I try tu update the field
with id_user_traffic = 11348 I obtain an error about key
duplicated.

SELECT oid, id_user_traffic, start_date, end_date
FROM user_traffic
WHERE id_user = 6738;

oid | id_user_traffic | start_date | end_date
---------+-----------------+------------+------------
1213776 | 11348 | 2003-03-07 | 2003-04-07
1213776 | 11348 | 2003-03-07 | 2003-04-07
1213776 | 11348 | 2003-03-07 | 2003-04-07
1213776 | 11348 | 2003-03-07 | 2003-04-07
1107090 | 9675 | 2003-01-17 | 2003-02-17
1213779 | 11349 | 2003-04-07 | 2003-05-07
1213782 | 11350 | 2003-05-07 | 2003-06-07

How is it possible have the oid and the id_user_traffic (
serial primary key ) duplicated ? Any idea ?