If you have access to a linux box, try pulling a sniffer on it, looking for dropped packets or mismatches. Bad ethernet card/driver possiblity.

I noticed some wierd stuff talking to the empeg over a transparent firewall bridge (don't ask... I just needed an ip addressable machine to play with, and guess what happened to be around.) Turned out to have a marginal ethernet card in the bridge, giving the errors. Doing a TCPDUMP on the connection was pretty interesting..