This sounds like one of the possible symptoms from having your
Ethernet cards misconfigured.  You should check that both ends (client
and server) are set to full-duplex mode, or both to half-duplex.  (If
you're using a dumb passive hub, they have to be half-duplex.)  If
they have conflicting configurations, you'll see tons of `late
collisions', which will show up as CRC errors on the Tulip chips.