This particular save of mine is kinda broken and I have no idea why. It just broke one day and I can't even save it without a ton of trouble.
I can't decipher what's breaking it, whether it's my C1000, corruption or TPT just being weird.
I doubt corruption as I can load it perfectly fine.
Can you try to open it in snapshots or jacob1's Mod and see if it works?
Normally saves which require newer features throw an "requires a new verison" error but this is different. It could be just a corrupted save or maybe a save that requires a new version which could be opened in c1000, jacob1 or snapshot verison.
I use C1000 and it opens perfectly fine, the save is still there. It just doesn't like to save for some reason, and throws an error every time I try to update it
Okay, I have released a small patch that fixes the issue. Thanks for reporting.