Can NOT dump db with 6.4.2's pg_dumpall

Hi,

In order to upgrade from 6.4.2 to 6.5.2, I tried to dump my db by typing

[postgres@redhat60 pgsql]$ pg_dumpall -z > db.out

Instead of getting a dump file, I got the following message.

========================================================================
pg_dump: The -z option(dump ACLs) is now the default, continuing.
SET TRANSACTION command failed.  Explanation from backend: 'ERROR:
parser: parse error at or near "transaction"
'.
pg_dump failed on cqn, exiting
========================================================================

My working platform is: RedHat Linux 6.0 with kernel 2.2.5-22 on a P-200
machine with 49M RAM.

Can anybody help?  Thanks in advance.

Michael