pg_dump and pg_dumpall fail when trying to backup database

I have a database in pgsql (7.3.2) on redhat 9.

When I try a 'pg_dump mydb' to back up the database, I get:
pg_dump: could not find namespace with OID 2200

Verbose version is:
-bash-2.05b$ pg_dump -v mydb | more
pg_dump: saving database definition
pg_dump: reading namespaces
pg_dump: reading user-defined types
pg_dump: could not find namespace with OID 2200
pg_dump: *** aborted because of error


Otherwise the database works just fine for daily use..etc,
just it cannot be backed up.

Anyone have any idea what is happening, or how to fix it?

Thank you!
Jack