Other mistake: Toward the end of the movie, as Johnny Depp and his leading lady are being led down into the dungeon, you can actually see the camera bouncing and shaking and hear it hitting the stairs as it moves down the stairs.
Other mistake: When Corso returns to Baroness Kessler's office he places his photocopy of the first engraving next to her book and you can see that the captions are not the same, yet neither of them notices. (01:24:15)
Answer: Lucifer was also known as the morning star. Depending on your view he passed the trial and was granted entrance through the ninth gate.