I just donated, please do one more fix so it no longer crashes in version 0.2.1B. Since zep promised the API is now stable that hopefully means no more updates necessary.
I think I can almost replicate the error. It seems to only appear when I have the cart saved locally by favoriting or saving it and not running directly from splore. I open the first door and walk left to the machines and then back. Then this message pops up.