What does this error message mean?

[Martin McCormick]

A Fluke Network tester is unable to get a DHCP lease on a given
network and keeps declining every lease offered to it by
dhcpd3.3.1. If everybody was declining leases, I would think we
had a rogue dhcp server, but a sniffer capture shows there is
none. The message reads:

dhcpd: DHCPDECLINE of 64.112.253.43 from 00:c0:17:b6:1a:06 via em0: not found

	On a different subnet, we saw an Iphone decline one
lease which was reported "abandoned" afterward and it did
successfully obtain a lease on the next try so I don't think
that is the same problem.

	Interestingly enough, the Fluke did obtain a lease on
one of the other subnets but it absolutely refuses to take any
lease I offer it when talking directly through the interface.
Other systems in the same subnet as the actual em0 interface
work normally.