According to Honky Tonk Man and PWTorch, KANE is in the middle of a contract dispute with WWE. Apparently, he has taken a big pay cut in his new contract, which he is not happy with.
KANE is scheduled to play the main character in a WWE produced movie, which further complicates the situation. Although, his movie deal may be completely separate.
The situation will most likely be worked out, as WWE cannot really afford to lose KANE at this time, especially while he is in the middle of a giant storyline.
IP will watch this story closely, so keep it here for all the updates.