we need a basic bug reporting sop!
___________________________which av mac, os et?.
which port?
have you tried the other port?
have you tried it on another mac?
is it a hardwired cable.
have you tried it with a custom extension set where that is the only driver.
expect 50% of all mac peripherals to have problems with the printer port. (double failure expectations on AV machines)
i'd take the thing apart and clean it up inside once i checked everything else out. sounds like some kind of sensor glitch if it's not the serial communications.
my brain is fried, but that'd be a good start.
oh, yeah, did it work reliably before this cropped up?
think methodically, report back with details!
good luck!
jt ™