So I read http://www.gamesas.com/topic/1370110-impact-of-system-stress-scripting-errors-on-game-performance/ and the dreaded "assigning none" error apeared in my log. I quickly removed the script, saved the plugin, reopened it, and re-attach it again to the player reference in the quest

And now it doesn't work.

I've even tried to use debug.messagebox to give a very visible indication. No dice. It's as if the script is not attached to the player

I don't remember if I ever start the game before I re-attached the script. Can I just make a new quest and be done with it?

Sounds like a dirty save.

No, it's not. I know because I tried to load a save that I haven't fiddled with and it still doesn't work