I had this same exact problem! No Mentalmind and no TheImmortalLordAtlas, Difficuly settings are grayed out. Yes it is possibly the fact that we need these keys. How do we get them?
You get the keys by grinding the corresponding rep. Auchindon Instances give LC Rep, Coilfang Resivior instances give Cenarion Refuge rep, Hellfire Cit gives Thrallmar/Honor Hold Rep, If someone can help with the last set it'd be helpful. These are the only 3 i remember.