Network File Transfer Crashing

[Graeme]

Whenever I try to send data between two computers on the network, where the
data is over about 50Mb, the transfer begins,. but then both network cards
"crash" ie they stop working, and I have to disable then re-enable the cards
to get them back on the network. I thought that it was my network hub, but
they are now connected through a switch. The cables are less than 10m in
total. I had the two computers plus a router connected directly to the
network switch, but the problem exists even if I disconnect the switch so
that only the two computers are on the network. The problem still exists if
I connect the two computers directly using a cross-over cable.

Any ideas?

Graeme