Saku,
Can you please give us a little more information about what's happening? When I recreated this error, it is caused by something *very* specific - that is, using an old save after the game journal has had changes made to it.
First, were you someone who had access to the game when it was in its beta stage (I apologize for having to ask but we had many beta testers from our Kickstarter and since everyone uses different names across different platforms, it's gotten difficult to know who is who).
Second, were you loading the game from an existing save rather than loading a new game? Renpy will pull save data from anywhere it can find it which means that saves you had in place from the demo, from beta, or any time from now will still show as valid save slots. These saves will throw this error 100% of the time.
Can you please try to load a completely new game, get yourself all the way to the end of the common route, and tell me if the game still throws this error?
In the mean time, I will try to confirm with some of our other Mac users whether they are also having this same problem.
Thank you!
~Esh