Farallon and Asante do the same thing - bridge to localtalk. If I'm not mistaken, yours (iPrint) is the newest one of those that anybody made.
Apple has changed appletalk to working only via ethernet, AND it no longer broadcasts "who's out there" to other appletalk devices (except once at startup, or something like that). So, what happens is that these bridge devices are "forgotten" by OS X - that's the symptom you have. You should be able to turn off/unplug power to the printer and Farallon, wait 20 secs, repower and then Re-ADD the printr in Printer Setup and print until the next time it happens again.
An additional problem I have with my Farallon ethermac (before your iPrint) is that it's made for 10BaseT networks only -- when I changed a hub to a switch (which auto-senses 100/10 speed) in my network, the Farallon locked up because the switch thinks it is 100 speed. I can either buy an old hub (don't want to go backward) or share the printer from an OS 9 computer.
Hope this helps.