It's some kind of time related error. The game couldn't get your current windows time and date and just gave up.
I have no idea what could have caused it. Could be the game hitching crashing when you saved it, maybe you changed your timezone from previous save time,.. No idea.
That said, this is just an exception that should have no bearing on the integrity of your save file. I made a workaround that will show and "ERROR" text instead of the save date. Saving and and loading should work. Right now, I'm trying to think of a way to release this fix as a patch and not as a entirely new game upload.