Well, that’s partial progress at least. :(
This is the first report that we’ve had of this kind of a problem on a Mac; we’ve heard one similar report on a Windows machine, apparently due to a bug in the underlying library that RoboPaint uses to connect to the serial port. I have added this report to our bug tracker ( https://github.com/evil-mad/robopaint/issues/127 ), and may possibly have some ways to follow up a little later in terms of gathering additional logging data. Can I ask what Mac OS version you’re using?
In the mean time, I’d suggest trying
* A different USB port on your computer.
* The other two WaterColorBot control programs, RoboPaint RT and our Inkscape extensions.
