A closer analysis of Advani's utterances makes it clear that he is unhappy with Modi since the time the Gujarat leader started displaying his Prime Ministerial ambitions. Advani still considers himself as the most eligible PM candidate from BJP and finds it difficult to come to terms with his onetime acolyte challenging him in this race.
Advani knows, times have changed and the same BJP cadre that used to revere him, even more than Vajpayee, has changed tack and is vociferously demanding the anointment of Modi as PM candidate. It's a clear case of the mentor not comfortable with the disciple outgrowing in size compared to his guru.
But this is what politics is all about. It's cruel and waits for nobody. Advani will take time before he accepts this reality but the sooner he understands it better it is for his party.