This really isn't the right place for this question; ideally, you should discuss it directly on the game's creator's page.
In this case, I have some experience with Renpy, and the error message you're seeing is usually due to an incompatibility between the save file of the old version and the new version.
This usually happens when certain changes are made when developing the new version without considering how they might affect existing save files.
There's not much you, as a player, can do, as this relates to the developer's coding of the update. It's best to discuss it directly with the developer so they can learn how to minimize these types of errors.
What you could do on your end is start a new game from scratch with the updated version.