pgAdmin not starting my job

Hello,

I'm running PostgreSQL 8.3.7 with pdAdmin 1.8.4 on WinXPSP3.

I installed pgAdmin following the instructions here
<http://www.pgadmin.org/docs/1.8/pgagent.html> and here
<http://www.postgresonline.com/journal/index.php?/archives/19-Setting-up-PgAgent-and-Doing-Scheduled-Backups.html>.

I created a batch file to do the backup. When logged in as Administrator
and running the batch file it works. When opening a command prompt as
user postgres [runas /user:postgres cmd.exe] and executing the batch
file it works, too.

For both users the password is set in
C:\Documents and Settings\<UserName>\Application Data\postgresql\pgpass.conf

When registering the pgAgent service I use the postgres user account
that was created during the PostgreSQL installation process. The root
user for the database is also called postres.
pgAgent.exe INSTALL pgAgent -u postgres -p XXXXXX hostaddr=127.0.0.1 dbname=postgres user=postgres

The service is then manually started in the computer management
console. Successfully.

After setting up the job in pgAdminIII, I try to run it (via the
context menu) but nothing happens. "Nothing" means the backup is not
created, but the job status in pgAdmin is altered: "Last result" says
"Successful" and the "Last Run" time is updated.

The job was created as "Batch" kind and the batch script specified in
the job definition:
F:\Daten\Munnin\PostgreSQL\pgagent\backup.bat

So the question is: what am I doing wrong?

The PostgreSQL log file does not give any hints, even with
log_min_messages=debug5

Rainer