I just don't understand this at all. I'm playing on Normal difficulty as a custom mage with 4 life books and 1 each of the other available schools (for Node Mastery). I've been buttering up Horus and he's at the highest disposition level towards me, yet he WILL NOT ACCEPT ANY TREATIES? I don't know if this is a glitch similar to Gandhi in one of the original Civilization games where you get too nice with him and he gets super-aggressive (ironic for Mahatma Gandhi). Any clue what's going on?
*shrug* The diplomacy is very wonky in this game. I seem to recall that AI will not accept treaties before some arbitrary amount of time has passed since the beginning of the game, though I might be mixing this up with some other game (maybe Civ or Gal Civ).
Also, it doesn't matter how much a wizard likes you, every wizard has a hidden "Patience" value (for lack of a better name), which will generally go down during diplomatic discussions. The more they like you, the higher it can be, the less they like you, the lower it tends to be. They'll break off communications automatically when their patience runs out. Their patience for negotiations will slowly build back up as turns pass.
Ultimately, I'm not sure the treaties will do much for you anyway, so I wouldn't worry about them too much.