pg_dump - problem

Hi,

does anyone know why I can't dump my databases? At some it work at some I
get an error message like the following

pg_dump -v  -t test_table test_database
--  saving database definition
--  last builtin oid is 18539
--  reading user-defined types
--  reading user-defined functions
--  reading user-defined aggregates
--  reading user-defined operators
--  reading user-defined tables
getTables(): SELECT failed.  Explanation from backend: 'ERROR:  aclitemout:
bad ai_idtype: 17 '.

I am using PostgreSQL 7.1.3...

Any idea?

        Thanks
                Steffen