Cache lookup failed for relation message in PG 8.3.7

Any ideas why we would be receiving this cache lookup failed message?

PostgreSQL 8.3.7 64 bit, RHEL 5 64 bit OS

Linux hostname.net 2.6.18-92.el5 #1 SMP Tue Apr 29 13:16:15 EDT 2008 x86_64 x86_64 x86_64 GNU/Linux

<2010-02-07 08:05:36 MST>ERROR: cache lookup failed for relation 391262678
<2010-02-07 08:05:36 MST>STATEMENT: SELECT n.nspname as "Schema",
c.relname as "Name",
CASE c.relkind WHEN 'r' THEN 'table' WHEN 'v' THEN 'view' WHEN 'i' THEN 'index' WHEN 'S' THEN 'sequence' WHEN 's' THEN 'special' END as "Type",
r.rolname as "Owner"
FROM pg_catalog.pg_class c
JOIN pg_catalog.pg_roles r ON r.oid = c.relowner
LEFT JOIN pg_catalog.pg_namespace n ON n.oid = c.relnamespace
WHERE c.relkind IN ('r','')
AND n.nspname <> 'pg_catalog'
AND n.nspname !~ '^pg_toast'
AND pg_catalog.pg_table_is_visible(c.oid)
ORDER BY 1,2;

Thanks.