Just checking, but what's your "Path" listed as on that save file? I was reminded that if it's still marked as "???" then the save is too old to be compatible. But if it's happening on new saves, then something's broken somewhere along the way.
So the paths were listed as "???", which I had just assumed was because another path split was coming up and the saves didn't know what to list. I didn't mention it to begin with since 2/3 of the massacre saves I loaded with "???" worked (Both Oswin/Sal live and Both Oswin/Sal die), so I wasn't sure whether it had anything to do witht the error. I'll try starting that path again and see if that fixes it.