Courtesy of IMDB:
Morgan Creek Productions fired Paul Schrader after he had submitted a completed movie, saying that he had given them "footage without any of the bloody violence the backers had wanted". He had already made it clear in interviews that he was making more of a psychological drama than an all-out gore-fest. He was fired and Renny Harlin was hired to re-shoot the movie. Almost 90% of the movie was re-shot and at least two characters have been dropped from Paul Schrader's version of the movie. Following the lackluster reception to Harlin's version, though, Schrader's version was finally released as Dominion: Prequel to the Exorcist (2005).