[Exim] logwrite command not permitted when filter not runnin…

I'm puzzled:

% pwd
/home/postmast
% ls -l .forward
-rw-r--r-- 1 postmast mail 4311 Mar 29 15:32 .forward
% head -4 .forward
# Exim Filter

logfile /home/postmast/logs/filter.log 0644
logwrite "From $return_path $tod_full\nSubject: $h_Subject\n"
% grep postmast /etc/passwd 
postmast:*:212:20:Postmaster:/home/postmast:/usr/local/bin/bash
% exim -bt postmaster
postmast@???
    <-- postmaster@???
  deliver to postmast in domain anchor-vispadmin-1.mail.demon.net
  director = localuser, transport = local_delivery

then when mailed:

2001-03-29 15:37:39 14idYR-0003oj-00 == postmast@??? <postmaster@???> D=userforward defer (-11): error in filter file: logwrite command not permitted when filter not running as user

in configure:

DIRECTORS

userforward:
driver = forwardfile
file_transport = address_file
pipe_transport = address_pipe
reply_transport = address_reply
file = $home/.forward
no_verify
no_expn
check_ancestor
filter

TRANSPORTS

address_pipe:
driver = pipe
return_output

and

address_file:
driver = appendfile
delivery_date_add
envelope_to_add
return_path_add

So why is it giving the error:

2001-03-29 15:40:14 14idaw-0003ou-00 <= <> H=internal.mail.demon.net [193.195.224.3] P=esmtp S=3438 id=985876794.1024938.375@??? from <> for postmaster@???
2001-03-29 15:40:14 14idaw-0003ou-00 == postmast@??? <postmaster@???> D=userforward defer (-11): error in filter file: logwrite command not permitted when filter not running as user

Any help appriciated (I still haven't figured what uid it's supposedly
not running as... :)

D.

-- 
    David Sloan - Senior Mail and News Systems Admin - Platform Management
  Tel: +44 845 272 0666    Fax: +44 20 8371 1167    Email: dsloan@???