i played this on the 1st demo i think and got the "unknown error." With the new version I decided to look further into it and I'm not entirely sure what I did but here what i did, looked into the "show package contents", i opened "Contents-Resources-app.nw-save" and i think by doing this it made the game saveable, **I think** i don't know, mostly wanted to share how i fixed the problem
Well, that error occurs if the game tries to save while it's placed in a folder with certain restrictions, in which case moving it to a folder with less restrictions usually fixes the problem. I suppose there is a chance that looking into the folder in question may have removed the read-only restriction, idk