OK, try this. Can you replace the Extensions folder with this one attached and see if it makes any difference.
It is to be found at:-
Macontosh HD -> Library -> Java
What version of the OS are you on?
It might be worth searching for people who have had trouble with Serial <> MIDI with your version.
If this doesn't work then we might have to explore going directly into Ableton. I don't have it but I could download the trial version and see what can be done directly.
Extensions.zip (27.3 KB)