I'm running Netware 5 and VFP6 (SP3). We did have some problems at first with some lingering machines that had IPX/SPX netword protocal still installed. The routers didn't seem to really enjoy the chatty protocol. Once we removed IPX/SPX and used TCP/IP the routers didn't shut down the circuit anymore. The only problem we're experiencing once in a while is disconnetion from the internet. The message is displayed and no sooner than clicking on the OK button we're back on the internet.

But, you may want to look more at the protocols you are using or maybe look at the hubs, switches or router.