Vacuum error on database postgres

I'm running postgreSQL 8.1.4 on Red Hat Enterprise Linux 3.

Things have been working well for a while but in the last few days, I've
gotten the following error during a nightly vacuum.

  postgres=# vacuum analyze;
  ERROR:  duplicate key violates unique constraint
"pg_statistic_relid_att_index"

I can vacuum that table individually without problems.

  postgres=# vacuum pg_statistic;
  VACUUM
  postgres=# vacuum analyze pg_statistic;
  VACUUM
  postgres=#

I found a posting from 2004 that suggested the following query.

   postgres=# select starelid, staattnum, count(*) from pg_statistic
group by 1,2 having count(*) > 1;
   starelid | staattnum | count
  ----------+-----------+-------
       2608 |         3 |     2
      10723 |         7 |     2
      10723 |         4 |     2
      10723 |         5 |     2
      10723 |         2 |     2
      10723 |         3 |     2
      10728 |         1 |     2
      10728 |         2 |     2
      10728 |         3 |     2
      10728 |         4 |     2
      10728 |         5 |     2
      10738 |         1 |     2
  (12 rows)

I did delete exactly one of each of these using ctid and the query then
shows no duplicates.  But, the problem comes right back in the next
database-wide vacuum.

I think the objects are as given below.

  postgres=# select relname,oid,reltype from pg_class where oid in
(2608,10723,10728,10738);
           relname         |  oid  | reltype
  -------------------------+-------+---------
   sql_features            | 10723 |   10724
   sql_implementation_info | 10728 |   10729
   sql_packages            | 10738 |   10739
   pg_depend               |  2608 |   10277
  (4 rows)

I also tried reindexing the table.

postgres=# reindex table pg_statistic;
ERROR:  could not create unique index
DETAIL:  Table contains duplicated values.
postgres=#

Help!

Paul