Epson C826051 (PS Card User Manual page 12

For EPL-4000/4100/ActionLaserII users
If you are using your printer with more than one computer and you
are using an optional interface, you must use the PostScript CARD
with the optional interface.
If you are using more than one computer but not using an optional
interface, you must use the PostScript CARD with the serial
interface.
Precautions
Introduction vii