I have additional update.
I checked the link between the Arduino IDE application and my Arduino Leonardo board, and there is a connection. I can move the spinning motor when I send the command “SM 2000,0,-200”.
So the problem seems to be from the version of with the Inkscape application and/or the Eggbot Control extension.
I therefore tried installing Inkscape version 0.48.5-2X11 and Eggbot Control extension release 2.4.0, and now I have a different error message when I try to connect to my Eggbot from Inkscape Eggbot extension, as follows:
python: VERSIONER_PYTHON_VERSION environment variable error (ignored)
The fantastic lxml wrapper for libxml2 is required by inkex.py and therefore this extension. Please download and install the latest version from http://cheeseshop.python.org/pypi/lxml/, or install it through your package manager by a command like: sudo apt-get install python-lxml
The problem is clearly finding the right working combination between Inkscape and Eggbot Control extension for the Mac OS 10.14 or higher.
Any idea out there will be much appreciated.