mailman 2.0.11/exim problem

[Joachim Schwendtner <schwendtner@neuhofen.at>]

when I send a mail to the mailman-list nobody of the list gets the mail 
but the list owner gets the following information every 15 minutes.

2004-06-01 18:23:02 1BVALM-0000Bq-00 Neither the system_aliases 
director nor the
address_pipe transport set a uid for local delivery of 
|/var/lib/mailman/mail/wrapper post mailman

I installed mailman 2.0.11 with apt-get on a debian-woody / with exim. 
I did the configuration changes in exim.conf like it is described in
http://www.exim.org/howto/mailman.html

there is a user called exim and a group called exim on my server.

who can help me?

joachim