PG Agent update error

After doing fresh installation of v8.4 on ubuntu 10.4, I run StackBuilder Plus to update PG Agent.
In the process of installation, an installation error dialog displayed:

----------------
The installation of PG Agent return an error.

Click on the OK button to ignore and continue with any remaining installations, or click Cancel to abort the remaining installations.
Note that ignoring this error may result in failure of any later installations that depend on this one.
----------------

Quite frankly this message is rather silly:
1. It didn't specify reasons for the error, hence the user will not be able to tell the seriousness or whether the error will affect further installations.
2. So how can the user decides to ignore or abort?

Anyway I found out there is an installation log at /tmp/install-pgagent.log and here is the content:

Log started 07/16/2010 at 00:05:28
Preferred installation mode : unattended
Trying to init installer in mode unattended
Mode unattended successfully initialized
Executing /etc/init.d/pgagent stop
Script exit code: 0

Script output:

Script stderr:

Preparing to Install
Creating directory /opt/PostgresPlus/8.4SS/pgAgent
Creating directory /opt/PostgresPlus/8.4SS/pgAgent/bin
Unpacking files
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/bin/pgagent
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/bin/psql
Creating directory /opt/PostgresPlus/8.4SS/pgAgent
Creating directory /opt/PostgresPlus/8.4SS/pgAgent/lib
Unpacking files
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/lib/libcom_err.so.2.1
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/lib/libcrypto.so.0.9.7a
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/lib/libexpat.so.0.5.0
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/lib/libgssapi_krb5.so.2.2
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/lib/libk5crypto.so.3.0
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/lib/libkrb5.so.3.2
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/lib/libpq.so.5.2
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/lib/libreadline.so.4.3
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/lib/libssl.so.0.9.7a
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/lib/libtermcap.so.2.0.8
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libcom_err.so.2
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libcrypto.so.4
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libexpat.so
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libexpat.so.0
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libgssapi_krb5.so
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libgssapi_krb5.so.2
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libk5crypto.so
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libk5crypto.so.3
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libkrb5.so
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libkrb5.so.3
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libpq.so
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libpq.so.5
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libreadline.so
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libreadline.so.4
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libssl.so.4
Creating link /opt/PostgresPlus/8.4SS/pgAgent/lib/libtermcap.so.2
Creating directory /opt/PostgresPlus/8.4SS/pgAgent
Creating directory /opt/PostgresPlus/8.4SS/pgAgent/share
Unpacking files
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/share/pgagent.sql
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/share/pgagent_upgrade.sql
Creating directory /opt/PostgresPlus/8.4SS/pgAgent
Creating directory /opt/PostgresPlus/8.4SS/pgAgent/installer
Creating directory /opt/PostgresPlus/8.4SS/pgAgent/installer/pgAgent
Unpacking files
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/installer/pgAgent/createuser.sh
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/installer/pgAgent/pgpass
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/installer/pgAgent/startupcfg.sh
Creating directory /opt/PostgresPlus/8.4SS/pgAgent
Unpacking files
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/LICENSE
Unpacking /opt/PostgresPlus/8.4SS/pgAgent/README
Setting variable connection from /tmp/pgAgent/bin/psql -l -d postgres
Script exit code: 127

Script output:

Script stderr:
/bin/sh: /tmp/pgAgent/bin/psql: not found

Error running /tmp/pgAgent/bin/psql -l -d postgres : /bin/sh: /tmp/pgAgent/bin/psql: not found
Setting variable connection from /tmp/pgAgent/bin/psql -l -d postgres
Script exit code: 127

Script output:

Script stderr:
/bin/sh: /tmp/pgAgent/bin/psql: not found

Error running /tmp/pgAgent/bin/psql -l -d postgres : /bin/sh: /tmp/pgAgent/bin/psql: not found
Setting variable connection from /tmp/pgAgent/bin/psql -l -d postgres
Script exit code: 127

Script output:

Script stderr:
/bin/sh: /tmp/pgAgent/bin/psql: not found

Error running /tmp/pgAgent/bin/psql -l -d postgres : /bin/sh: /tmp/pgAgent/bin/psql: not found
Problem running post-install step. Installation may not complete correctly
/bin/sh: /tmp/pgAgent/bin/psql: not found
Problem running post-install step. Installation may not complete correctly
/bin/sh: /tmp/pgAgent/bin/psql: not found
Creating Uninstaller
Creating uninstaller 25%
Creating uninstaller 50%
Creating uninstaller 75%
Creating uninstaller 100%
Installation completed
Log finished 07/16/2010 at 00:05:33

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Is this a bug with the installation program? How can I install the upgrade?

Thanks.
Cheng-Hong