Djinn Raffo is very correct if u right click on a spell and memorize it then u need to rest before u r able to use it also as djinn said u cannot wear armour and expect to cast spells just simply remove the armour and cast but i would recomend not equiping armour on mages and the like as when in combat u cannot change armour so your spells would be useless..
I Will Come For You As My Sword Is My Witness..