The error appears when clicking on a few specific locations, not when loading. I checked the code and you do not set the variable before calling it. I downloaded from Mega, it's not corrupted. You can write the checksum in the OP so people can verify the downloaded file if that's your concern.
I read the hints, the hint says go to your PC, it does not say "you have to do X before going to PC". An exclamation mark appears in the PC icon, as there is an action to perform, but when you click, there is no task. If it's not a bug, it's a UX problem.
