pg_dump: SQL command failed

I am trying to take backup of postgresql 9.0 by using pg_dump command.
command here is:
cd /opt/PostgresPlus/9.0AS/bin and hit the following command

pg_dump -h xxx.xxx.xxx.xxx -p 5432 -U superuser db_name>db_name.dump

But i am getting error like,

pg_dump: SQL command failed
pg_dump: Error message from server: ERROR:  schema "dbms_sql" does not exist
pg_dump: The command was: SET search_path = dbms_sql, pg_catalog

please give me suggestion.