Corrected entry: In both instances where William crossed the English Channel, it was on a chain ferry. It is highly unlikely that any individual, or even a group of individuals could afford the 20-odd miles of chain it would require. To top it off, when they return to England, their landfall is made at London, which would require yet another 20-odd miles of chain to take them up the Thames.
Corrected entry: William uses Sir Ector's armor, which still has his device (the emblem on the shield) painted on it. Since Sir Ector was a regular on the jousting circuit, other knights and nobles would have been able to identify the device and expose 'Sir Ulrich von Lichtenstein' as an imposter.
Corrected entry: The Royal Guards who arrested William wore a Spanish helmet. This helmet actually didn't became in fashion until the time of Elizabeth the First, 200 years later.
Corrected entry: Before the companions reach Paris, there is a camera shot which includes the Eiffel Tower. It would be factually inaccurate to place both Chaucer and the Eiffel Tower in the same place at the same time seeing as though Chaucer was around centuries before the Eiffel Tower was constructed to mark the centenial year of French Independence, in 1889.
Corrected entry: In the first jousting scene after William is given his new armor from Kate, Roland and Wat lie to him about his next opponent having raised his country's taxes to pay for the tournament and then cut to a shot of his opponent trying to mount his horse. The problem is he mounts the horse from the wrong side. The knight should have mounted from the left side but can plainly be seen mounting from the right. Mounting from the left is an equine tradition dating back to the times of knights and is done because the sheath of a sword is worn on the left and gets in the way if they try to mount from the right. Surely a knight would have known this.
Corrected entry: When William is facing Adhemar in the final match, Adhemar almost destroys Williams' frontal armor's right side (you can even see it is folded in two). When they are preparing for the second round his armor is intact again. When the second round begins, back to the destroyed armor. (01:58:20)
Corrected entry: In the opening sequence when the captions come up "In medieval times, a new sport emerged...", we see a knight being knocked off his horse in a joust. The knight being knocked off is wearing Heath Ledger's original suit of armor. (You can tell by the shield he is holding - it has the three phoenixes on it.)
Corrected entry: The redheaded peasant Wat constantly carps on about not having enough money to eat yet he wears a rather modern very thin silver chain throughout the entire film. Perhaps he could have pawned that to buy some Tansy cakes with peppermint cream?
Corrected entry: When there was a flashback to when William was a child, the child actor used looked exactly like the adult actor...with one major flaw: The boy had sparkling blue eyes, the man, dark brown.
Corrected entry: During the pub scene when the French drunkards are challenging Chaucer and the others to bet that Ulrich will not win the tournament, Wat throws a fit and calls one of them Quasimodo. Quasimodo is a character from "The Hunchback of Notre Dame" by Victor Hugo, published in 1831 - about 500 years later. Even if Quasimodo had been based on a real person, the story took place in the 15th, not 14th, century. (01:15:55)