[Exim] Odd error

Anybody know what causes the following error in exim 4.3

2004-03-09 16:54:29 1B0kUu-00040I-0R unable to set gid=501 or uid=100
(euid=102): local delivery to ron <Ron@???>
transport=local_delivery
2004-03-09 16:54:29 1B0kUu-00040I-0R failed to read delivery status for
Ron@??? from delivery subprocess
2004-03-09 16:54:29 1B0kUu-00040I-0R appendfile transport process
returned non-zero status 0x0100: exit code 1
2004-03-09 16:54:29 1B0kUu-00040I-0R == ron@???
<Ron@???> R=localuser T=local_delivery defer (-1)
2004-03-09 16:54:29 1B0kUu-00040I-0R Frozen

I can deliver the message with an exim -M though.

Ron

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Ron McKeating
Senior IT Services Specialist
Internet Services and Software Solutions
Loughborough University
01509 222329