Not sure, but here is something to try
PCMCIA Multifunction Card Issues
SocketCom ES-1000 Ethernet/RS-232 card (Brian Candler)
Date: 2000, May 26
From: David Hinds <firstname.lastname@example.org>
module "pcnet_cs" opts "use_shmem=1"
in /etc/pcmcia/config.opts, to make the card use a shared memory
window for packet transfers.
Sorry, that's not it by Brian Candler, 2000, May 28
Got it!! by Brian Candler, 2000, May 31
Spoke too soon by Brian Candler, 2000, May 31
to: "Not sure, but here is something to try"