failure with pg_dump

Hi:

I have a script that I use to do regular dumps of my database. Over the
weekend it failed, and produced the following error message. I'm not
sure why this would have happened, how I would find out which index is
referenced by 136451098, or where this select came from.

pg_dump.sqlhost: Error message from server: ERROR: cache lookup failed
for index 136451098
pg_dump.sqlhost: The command was: SELECT t.tableoid, t.oid, t.relname as
indexname, pg_catalog.pg_get_indexdef(i.indexrelid) as indexdef,
t.relnatts as indnkeys, i.indkey, i.indisclustered, c.contype,
c.conname, c.tableoid as contableoid, c.oid as conoid, (SELECT spcname
FROM pg_catalog.pg_tablespace s WHERE s.oid = t.reltablespace) as
tablespace, array_to_string(t.reloptions, ', ') as options FROM
pg_catalog.pg_index i JOIN pg_catalog.pg_class t ON (t.oid =
i.indexrelid) LEFT JOIN pg_catalog.pg_depend d ON (d.classid =
t.tableoid AND d.objid = t.oid AND d.deptype = 'i') LEFT JOIN
pg_catalog.pg_constraint c ON (d.refclassid = c.tableoid AND d.refobjid
= c.oid) WHERE i.indrelid = '136451090'::pg_catalog.oid ORDER BY indexname

Any help would be greatly appreciated.

Mija