If you don't mind being a guinea pig, this version has a little bit of debugging code in it. (I can stop the error happening, but I don't know exactly why it's happening. I just have guesses.)
It should print out an error when it scans the quest log. I think I've added all the relevant information into the error message, so...
(I'd do it myself, but none of my characters have a quest that trips this bug.)