I found exactly where the issue is: you have to save between getting your background and either ending chapter 1 or going into the VIP room for the error to trigger.
It's very specific which is why none of the poeple playtesting it found it.
Now that i identified the source of the issue I'm rolling out a 0.6.1.2 that should fix the bug so it doesn't happen to anyone else, AND would handle your messed up save file so it doesn't throw an error, no work on your part. There's nothing wrong with the save file itself so don't worry about that, renpy just has a hard time parsing the save name.
Sorry for the inconvenience and thank you for helping me fix this.