The message isn't part of my code, it's part of the Renpy engine, on which my game is built.
Usually, the save incompatibility issue comes with a "couldn't find a point to roll back to" message. So... I'm not sure what is really going on there. The game should give you an error log, could you please forward it to me?
You can message me on Discord if that is easier for you.
Thank you in advance.