Bad packet errors only on one iMac on the network

I'm having a wierd problem with my new 24" aliminium iMac. I'm getting quite a few of the following in the system log:

kernel[0]: AppleYukon2 - bad packet received. length: 60, packet status bits: Good flow-control packet

All my machines are connected via a Netgear GS724T managed gigabit switch, which in turn connects to an ADSL2+ modem/router. An older 17" iMac doesn't get these errors. I've tried a brand new cat 6 tail from the switch directly to the 24", and plugged each iMac into the other's port on the switch. So I've eliminated any cabling errors.

Would this indicate a hardware fault on the 24" or could there be some other cause I can investigate?

Thanks for any help.