GUI Pie v3 brought in many changes, including to the way the exported code runs. This means that main project files written for files generated by GUI Pie v2.8 or earlier will not work with files generated in v3.
Luckily, migrating is easy! Your save files will be automatically updated upon opening them in v3. All that needs to be done is to update your main project files. Follow these old/new patterns to upgrade your scripts:
Importing:
Old: from gui import *
New: from gui import gui
Initialising:
Old: gui.initModules()
New: <delete this line>
Running:
Old:
while True:
gui.run()
New:
gui.run()