Thank you! Yes, I was playing with a save from the older version.
I wasn't sure exactly what to do, but what I ended up doing was clicking "open" on the "an exception has occurred" error page, deleted the text in the plain-text window that popped up, copied and pasted the text from the plain-text file in the link you posted into the empty window, saved & closed the window, saved & quit the game, and when I opened it back up it worked!
Thanks again.