Most RenPy games work just fine for me.
Well my first guess would be that it's a file path naming issue going on, as I was able to get that error by intentionally adding special characters in some of the parent folder names (and it's the only time I've ever seen it from a renpy game.)
If you haven't already, re-download the game just in case, and try running it from a different partition, off a usb key, or just a different base folder in your comp, making sure the full file path to the game is something that's Windows friendly (letters & numbers, with spaces being okay as well.) Yes, it's Linux, but I've noticed some special characters cause issues where others don't, so "Windows friendly" seems like a good troubleshooting option.
Hopefully it's just a simple fix like that, as I haven't touched a Ubuntu-based distro in ages so I wouldn't know where to go from there.