Xbox 360 ‘The Fallen’ / ‘Season Unending’ Glitch Help

[hekalopter]

I’m currently having problems with the quests ‘The Fallen’ and ‘Season Unending’ in Skyrim on Xbox360; I cannot complete ‘Get Greybeards help in negotiating a truce’ as when I do, I am told to talk to Ulfrec and Tullius. When I talk to Ulfrec he says he will come to the negotiations, and the marker shows this as complete. However, when I try talking to Tullius, no options related to the truce/treaty come up. I’ve already completed ‘The Jagged Crown’ and given the crown to Tullius, and have taken the oath. I don’t have the earlier save files, and I’m currently level 40 and would rather not start a new game.
I’ve searched everything I can find on this topic and nothing has worked to solve this. Possibly relevant: I have the quest ‘Paarthurnax’ but I have not yet killed him.
Any assistance would be very much appriciated.