From a support forum for a similar problem:
This sounds like a link reset. Easiest way to find out is to grab an 8-port switch, and plug all the machines into that, then uplink to your router. If it is the router that's breaking things, this should isolate it. If it doesn't fix it, you could always return the switch.
From a support forum:
I have the same problem and found the problem is down to the Broadcom cards. In my case it is IBM servers connected to CISCO 3750 switches. When Auto sense is set, the Broadcoms cause the switch to reload. After setting the speed to 100 Mbps full the problem seems to be better but still getting the odd reload.