I was having this problem too (Mac wouldn't start up with the Z-Stick plugged in). I tried the PRAM reset, which did not help. I got a replacement Z-Stick, and was still seeing the same problem. Then I tried changing USB ports, and now it works as expected. I moved from a port on one far end of the row of ports, to a port on the other end. Maybe a separate bus? Maybe something else on that bus was causing a conflict? In any case, for others seeing this issue: try a different USB port before trying a new Z-Stick. And maybe try unplugging all the other USB devices too, to reduce variables.
Thankfully I'm just getting started and only have 2 devices I had to exclude / re-include.