Did you click yes? That's a message from the renpy engine itself and it's saying that your save was created on a different device. Maliciously constructed save files can harm your computer. If you trust it, you can click yes, I can only assume that it'd let you open your save.
Not sure, I haven't been prompted with that message before. Did you transfer your save from like a laptop to a PC or something? I can only suggest finding a solution on Google from other renpy games.
