This message comes up when the Macintosh is trying to use the Printer Port for
a LocalTalk (network) connection and the Apple IIe card is trying to use the
port for serial data. This resulting conflict causes the "Printer Port is
already in use" message.
If you are connected to a LocalTalk network in the Printer Port, use the
"Network Printer" icon and not the "Printer Port" icon in the Slots menu. See
the manual for information on selecting the network printer.
If you are connected to a serial printer in the Macintosh printer port, return
to the Macintosh Chooser and select "AppleTalk Inactive". This removes the
conflict, and the port-in-use message will no longer appear when you start the
IIe application.