[Exim] Appendfile/Local delivery problem

Folks,

here's a problem with local delivery. Sometimes it works, sometimes
not, as you can see.

gid 12 = mail
Exim runs as user "exim" but has +s flag set
The spool-file is 660 and is owned by the user itself with group mail.

2002-03-07 17:44:31 16j0tT-0000h5-00 Unfrozen by forced delivery
2002-03-07 17:44:31 16j0tT-0000h5-00 Unable to get root to set uid 543 and
gid 12 for local delivery to thomas.reyers: uid=550 euid=550
2002-03-07 17:44:31 16j0tT-0000h5-00 failed to read delivery status for
joe.average@??? from delivery subprocess
2002-03-07 17:44:31 16j0tT-0000h5-00 appendfile transport process returned
non-zero status 0x0100: exit code 1
2002-03-07 17:44:31 16j0tT-0000h5-00 == joe.average@???
T=local_delivery defer (-1)
2002-03-07 17:49:56 16j0tT-0000h5-00 Unfrozen by forced delivery
2002-03-07 17:49:56 16j0tT-0000h5-00 => joe.average
<joe.average@???> D=localuser T=local_delivery
2002-03-07 17:49:56 16j0tT-0000h5-00 Completed

Anyone with any idea?

Thanks
Sascha