Hello.
What targets are you trying to set with the Set Target command? Are you aware that the units are quarter-microseconds? It would be helpful if you could post here a screenshot or text version of your shell session showing how you reproduce the problem, with comments about when you unplugged or plugged in the Maestro. This would let us see exactly what you are doing and what your program is printing.
Here is another thread where someone was controlling a Maestro with Python, which might be useful to you: Micro Maestro USB on Mac
–David