He is only infallible under certain very limited circumstances, and the main criterion is that he be teaching in conformity with the universal and ordinary magisterium of the Church which means "what has been taught always and everywhere by all the faithful." By definition, it can never be infallible if or when the pope teaches a novelty. For example, the Immaculate Conception was not a novelty. Catholics had always believed it. It was being celebrated as a feast day in Mexico when the Virgin appeared at Guadalupe, 350 years before the infallible pronouncement of the doctrine. But later it was defined by the pope as dogma.
That's been a mainstay of Roman Catholic doctrine for centuries, so either that "truth" has changed, or the "truth" about salvation only being available through the Roman Catholic Church has changed, or Pope John Paul II is a false Pope.
When a pope teaches in contradiction to centuries of Catholic doctrine, it is a source of grave scandal. That is why Mel Gibson practices the traditional Catholic faith, not the Vatican II version.
Sounds like two denominations...