The week before when Eric was HOH, Eric told Kaysar that if he kept him safe that Kaysar would do the same for him next week. Kaysar did swear on his life but also asked that Eric not go after Michael. Kaysar would not play for Michael because he did not want to interfere with Eric. When Kaysar nominated James and Maggie, he had a one on one with Eric and Eric said he would not interfere with the POV, which he was already campaiging to get James out and said he would play for Kaysar and not use the veto. Eric had broken 3 deals with Kaysar by then so Kaysar put him up do to his "dirty" play.
Also, Kaysar and Eric never discussed that Eric would be not be chosen as an alternate nominee.
....Did Kaysar ever really promise Eric that he wouldn't put him up? I don't remember seeing that but some people have said otherwise