ERROR: cache lookup failed for type 16292881

Since a few days ago we are having problems while performing backup using
pg_dump to a PG 8.4 database over a Centos 5.5
There are several databases in this server, but this is the only one that
produces this FAIL.
Reported message from pg_dump is:

*(...)*
*pg_dump: reading triggers for table "usuario_sistema_externo"*
*pg_dump: reading dependency data*
*pg_dump: saving encoding = UTF8*
*pg_dump: saving standard_conforming_strings = on*
*pg_dump: saving database definition*
*pg_dump: SQL command failed*
*pg_dump: Error message from server: ERROR: cache lookup failed for type
16292881*
*pg_dump: The command was: SELECT proretset, prosrc, probin,
pg_catalog.pg_get_function_arguments(oid) AS funcargs,
pg_catalog.pg_get_function_identity_arguments(oid) AS funciargs,
pg_catalog.pg_get_function_result(oid) AS funcresult, proiswindow,
provolatile, proisstrict, prosecdef, proconfig, procost, prorows, (SELECT
lanname FROM pg_catalog.pg_language WHERE oid = prolang) AS lanname FROM
pg_catalog.pg_proc WHERE oid = '16292882'::pg_catalog.oid*
*pg_dump: *** aborted because of error*

We 've found no one type with this OID.
Looking at a solution in several forums, speaks about objects dropped in
replication platforms, but it is not this case.
Any help to know where to look for?
Thank you..

Ramiro Barreca
rbarreca(at)gmail(dot)com