What is the ruling on praying behind an Imam who mispronounces Al-Fatiha (he reads "a'mat alayhim" instead of "an'amt alayhim"), and insists on leading the prayer despite the presence of someone more qualified, and what is the ruling on warning worshippers not to pray behind him?

If a person does not recite Al-Fatihah well, then it is not permissible to pray behind him. He must be advised to learn it. If he insists on his mistaken view, then worshippers must be warned against him and he must be prevented from leading the prayer, due to the saying of the Prophet, peace and blessings be upon him: "The one who recites the Book of Allah best should lead the people in prayer," and his saying: "There are three whose prayers do not rise above their ears: ... and an Imam who leads people while they dislike him."