f5soh,
Thanks for your reply.
The issue I see, is that you can't use the GUI included in the GitHub zip file, you will get the error, but if you upload the .Hex file from the wiki, the GUI will work, both of them, the one that comes with the GitHub Zip and the one from the wiki.
Looks like the firmware on the GitHub was updated but not the GUI.
I look it and it was touched couple of month back, at least the Firmware
I will try to contact the developer and see if he has some inside input