If you have attached your LaserWriter to an MS-DOS computer which has an
AppleTalk PC card, and you are running your Macintosh in serial port
configuration, and printing to a LaserWriter IINT or LaserWriter IINTX, you
may find that the LaserWriter icon appears and disappears at random.
This will probably be true for all other Macintosh computers on the
network. As you watch the Choosers, the LaserWriter icons may appear and
disappear with no obvious pattern.
This is a normal response to an unworkable configuration. Because of this
problem (and possibly others), the "LaserWriter IINT-NTX Owner's Guide"
warns that you should disconnect any serial cable attached to the printer
before using LocalTalk, and conversely that you disconnect the LocalTalk
cable from the printer before connecting a cable to the RS-232 serial port.
See the appendix on Connecting to and Printing With an MS-DOS Computer in
the "LaserWriter IINT-NTX Owner's Guide" for more information.