OK, I hadn't tried to kill the pope yet. Perhaps that's the answer!!!

About ceasefires... I've noticed that I can't offer a ceasefire to ANY Catholic faction. Not that they won't accept it, I just can't even OFFER it, it doesn't appear in my options. Is that not a result of the crusade? I also can't offer an alliance with any catholic faction either.

Strangely, the AI can approach ME and ask for a ceasefire, but I can't do the same to him next turn. I had just assumed it was the Crusade thing... is that not the case? If not what else affects whether or not I can even offer a ceasefire?