Odd pg dump error: cache lookup failure

My pg_dump scripts have been bombing lately, and this is the error I see a
bit into the backup process:

pg_dump: error: query failed: ERROR: cache lookup failed for attribute 1
of relation 1152770777

pg_dump: error: query was: SELECT t.tableoid, t.oid, t.relname AS
indexname, inh.inhparent AS parentidx,
pg_catalog.pg_get_indexdef(i.indexrelid) AS indexdef, i.indnkeyatts AS
indnkeyatts, i.indnatts AS indnatts, i.indkey, i.indisclustered,
i.indisreplident, c.contype, c.conname, c.condeferrable, c.condeferred,
c.tableoid AS contableoid, c.oid AS conoid,
pg_catalog.pg_get_constraintdef(c.oid, false) AS condef, (SELECT spcname
FROM pg_catalog.pg_tablespace s WHERE s.oid = t.reltablespace) AS
tablespace, t.reloptions AS indreloptions, (SELECT
pg_catalog.array_agg(attnum ORDER BY attnum) FROM pg_catalog.pg_attribute
WHERE attrelid = i.indexrelid AND attstattarget >= 0) AS
indstatcols,(SELECT pg_catalog.array_agg(attstattarget ORDER BY attnum)
FROM pg_catalog.pg_attribute WHERE attrelid = i.indexrelid AND
attstattarget >= 0) AS indstatvals FROM pg_catalog.pg_index i JOIN
pg_catalog.pg_class t ON (t.oid = i.indexrelid) JOIN pg_catalog.pg_class t2
ON (t2.oid = i.indrelid) LEFT JOIN pg_catalog.pg_constraint c ON
(i.indrelid = c.conrelid AND i.indexrelid = c.conindid AND c.contype IN
('p','u','x')) LEFT JOIN pg_catalog.pg_inherits inh ON (inh.inhrelid =
indexrelid) WHERE i.indrelid = '1152770777'::pg_catalog.oid AND
(i.indisvalid OR t2.relkind = 'p') AND i.indisready ORDER BY indexname

Any ideas on what this might mean, or where to look?

--
Wells Oliver
wells(dot)oliver(at)gmail(dot)com <wellsoliver(at)gmail(dot)com>