AttributeError: 'gtk.Button' object has no attribute 'confirm'

[yush]

On ubuntu 18.04, with Graphtec 330-20, I installed graphtecprint as said in README. (+copy gtp_loader.py and cameo.py into /usr/local/bin). When I use graphtecprint < test.ps, the GUI appeared with the right preview and the plotter is found

. But when I click on Print I run into the following error.

Traceback (most recent call last):
File "/usr/local/bin/graphtecprint", line 152, in on_okbutton1_clicked
w.confirm()
AttributeError: 'gtk.Button' object has no attribute 'confirm'

Is there a way to make it work ?

Thank you.