[Exim] Does anyone know the difference?

Hi,

does anyone know the difference between exim accepting mails from another
server and delivering them immediately and putting them in the queue and
waiting for the next queue runner to deliver them.
I'm running exim with the arguments "-bd -q5m", and for some reason exim
still puts all mail in the queue with the msglog message "defer (-1)" and
"unable to set gid=101 or uid=501 (euid=501)". Those are the IDs exim is
running under and the IDs the virtual mailfiles belong to. Next time the
queue runner passes by, all mail is delivered without any problems.

Thanks for your help

DANIEL