Other mistake: It's revealed that the Knights who say Ni can't say "it" (at least, after they become the Knights Who Say... that other thing), but they still say "it," most notably when they're telling Arthur to place the second shrubbery next to the first one - "When you have found another shrubbery, you must place IT here, beside this shrubbery..."
Suggested correction: They aren't the Knights Who Can't Say "It" - they are the knights who are determined to be a pain in the **** regardless. They are going to be as big a nuisance as they can to anyone who comes along and pretending they can't say "it" is just their latest tactic.
Other mistake: In the early scene where the submarine has surfaced, titanosaurus emerges from the water and seems to be standing on the ocean floor. Just a few minutes earlier, the sub was at a depth of 250 meters, ergo the dino has to be walking on water.
Other mistake: Clay Tanner plays Jack Henderson in this film, yet the end credits list him as "Delbert".