NO_TEXT_FOR_KEY CB. It's right there in the screenshot.What CB was it?
Even better, the war ended instantaneously and it was against his liege. That's a pretty difficult situation to engineer. (Because, in most cases, when you declare war on your liege you become temporarily independent. I can only think of one way this could happen: if you were an active participant in the same war as your liege and, while that's going on, the "press unlanded courtier's claim" event fired against your liege. Doesn't explain the NO_TEXT_FOR_KEY though ;-p )