Corrupted db?

We got a problem ticket from the customer.
Messages in the error_log indicated problem trying to insert
a duplicate value into a table.

Looking at the database (v.7.3.2 on Solaris) I'm puzzled with this:

syncdb=# \d
ERROR: Cache lookup failed for relation 17075

syncdb=# \di
ERROR: Cache lookup failed for relation 17081

syncdb=# \d property_types;
ERROR: Cache lookup failed for relation 17075

syncdb=# \d public.property_types
Table "public.property_types"
Column | Type | Modifiers
-------------+-------------------------+-----------
id | integer | not null
name | character varying(256) | not null
stamp | date | not null
description | character varying(1024) |
Indexes: pt_pk primary key btree (id),
pt_name_uid_uk unique btree (name)

syncdb=# SET search_path = public, pg_catalog;
SET
syncdb=# \d property_types;
ERROR: Cache lookup failed for relation 17075

syncdb=# select * from pg_namespace ;
nspname | nspowner | nspacl
------------+----------+--------
pg_catalog | 1 | {=U}
pg_toast | 1 | {=}
public | 1 | {=UC}
pg_temp_1 | 1 |
(4 rows)

syncdb=# select * from property_types;
id | name | stamp | description
----+------+-------+-------------
(0 rows)

INSERT INTO property_types (id, name, description, stamp)
VALUES (nextval('pt_seq'), 'FROM_RELATIONSHIP',
'Describes the relationship of ...', date('today'));

ERROR: Cannot insert a duplicate key into unique index pt_name_uid_uk
---------------------------------------------

I can only guess that something is corrupted.
What could lead to that?
Can this can be prevented or repaired?

Thank you,
Mike.