Hmm, that's strange >.< Do you know which version you originally downloaded? Because if it was from before I updated all the files with the most recent demo version late last year, that might be the cause! Cos I had to rename stuff and delete other stuff that was no longer relevant.
The latest version is the one called 'Darling Duality - Demo - (Windows/Mac/Linux)' and because so much was changed in that version, it means save files from the older versions can't be carried over cos they would just break the game >.<