I've read over this thread and tried several suggestions, including using a second save (save_1) instead of one save (save_0), which didn't work, amongst other things that all failed, so I don't know what the problem is.
http://www.gamefront.com/files/24310105/save_1.rar
It's a fresh save with no mods at the very beginning (level 15, 14 skill points available, 1 flexible hose, 1 clamp, no money, et cetera), and John's my character.
Like I said, the character doesn't matter because I get the error with any of the characters, and the error shows if I try saving whether I press the Unlock Skills button just for the character, Unlock All Skills button, or even just unlock a single skill for any of the characters.
If you can make it work, I just want all of John's skills unlocked but not maxed out.
EDIT: I've made multiple new saves and always got this error. And it's not just my saves either. I've downloaded others' saves from this thread and got the same error. I've run the installer and program both normally and as administrator as well so that's not the issue either.