In the beginning as Robin approaches the ambush scene he is seen running with his bow in hand, arrow at the ready. As the camera switches away then back he is seen taking his bow off his back.
When Robin first discovers the inscription on the sword hilt in the boat, the inscription reads from the base of the blade to the pommel. But when he re-reads the inscription by the fireplace on his first night in Nottingham, it reads from the pommel to the base of the blade.
Near the beginning of the movie when Marian is helping the men plow the field, a thunderstorm is approaching behind her (as evidenced by the dark clouds and thunder). Yet a few minutes later when the sheriff begins harassing her, we only see puffy white clouds and blue sky.
When riding to board the boat in France, Robin's horse is already wet from the mid tail down, while the other horses are dry.
When Robin is drawing back an arrow to shoot at Godfrey, there is no blood on his hand when the camera is on the arrow, until the next shot, where his knuckles are bloody.
Richard states he can't wait to lock his mother and brother up. In fact, Richard and his mother were quite close. She had been imprisoned by her husband, Henry - and one of Richard's first acts as King was to order her released.
Though there are primary sources dating back to within a few years of when the film takes place which describe landing craft that "had doors, which were easily opened, and a bridge was thrust out whereby the knights could come forth to land all mounted", these doors were in the stern of the ship, not the bow, and were not intended for amphibious landings. [William of Tyre, Chronicon, ed. Robert B. C. Huygens (Turnhout: Brepols, 1986), p. 927]
In reality, Richard died in the arms of his mother, after a wound from an arrow became gangrenous.
In the movie King John refuses to seal the Great Charter (Magna Carta). In reality he sealed it, even though he later sought support from the Pope to annul it.
It was the Barons who actually invited Prince Louis (son of the French King) to invade England, due to King John's efforts to annul the Great Charter (Magna Carta).
From 1066 until 1399, English kings spoke French in their daily lives, and Latin in some diplomatic transactions. They usually did not even learn to speak English, which they regarded as a peasant language beneath their dignity. Their speaking English in the film is an acceptable artistic decision, consistent with all English and French characters speaking in modern, rather than medieval, standards of language.
Several characters speak of "seed corn." Many viewers interpret this as American maize which wasn't introduced to England until the 15th or 16th century. However, the word "corn" in 1199 England was used for many different cereal grains (wheat, rye, oats, etc.), not the corn-on the-cob we think of today.
The shields carried by the rank and file troops do in fact have uniform indentations in them. However, these are not meant to be battle damage. Medieval shields were constructed of thin sheets of wood glued together in cross-grain layers - literally, plywood. To increase durability, they were covered on the front with fabric or leather, sometimes with a a thin layer of padding in between, and then painted. The "holes" that have been pointed out are in fact where the rivets that attach the arm and shoulder straps (when not in use, the shield was slung over the back for easier carry) have indented the covering material. This is what gives the uniform appearance.
It has been said that the size of Robin's childhood hand mark on the carved stone when we see Robin's memory fits the size of his hand as an adult. However, Robin places his hand in the hand mark of his father which fits. When the marks are made, Robin (as a child) makes the mark on the left, while his father makes the mark on the right. It's the mark on the right that the adult Robin places his hand into.
When Robin is captured by the children of the forest and taken back to their camp, it is obvious that they are all wearing rubber feet to help protect them.
During the period in which this film is set, rulers would not have been called "Your Majesty," a term of address that was created in Tudor times. Earlier kings were addressed as "Your Grace."
When Robin and his men are on the ship from France to England, they are drinking out of glass goblets. Glass was very expensive, and would never have been used on a ship. Instead, they've have had pewter or wooden drinking vessels.
When the French king is preparing to land on the English Coast, he is told that they would land in "about 40 minutes". Time was not measured in minutes at that time. The closest they could tell was before mid-day or after mid-day.
The stone castles are of a style not seen until the reign of John's grandson, Edward Longshanks, and England was not known for its longbow archers until after the time of Edward as well. England got its longbowman from Wales as mercenaries until after the time of Wales' final defeat during the reign of Longshanks.
When Godfrey meets a Frenchman outside of a sleeping camp, he whistles and is answered with the the song Frere Jacques. The earliest known version of this song is from 1775.
In the Director's cut of the film on DVD, the French land in "Dungeness" (in the theatrical version it is never identified by name). Dungeness is a flat marshy area with no cliffs as depicted in the film. The area looks more like Dover, which would have been a more likely choice to invade since it is somewhat closer to France than Dungeness, although not considerably so.
At the meeting in Barnsdale, William Marshal informs King John and the Barons that the French are "in the channel". Then, after the battle at Nottingham, the French officer informs Robin that the French will land in two days. (aside from him having no way to know this since the message to Philip to invade had just been dispatched by Godfrey when they marched on Nottingham). The channel crossing from Calais to Dungeness is only about 25 miles and would not take two days.
Loxley's hall is said to be at Peper Harow. Peper Harow is actually a rural village in Surrey, south west of London and approx 150 miles from Nottingham.
In the establishing shot of King Richard's campsite in France, a burnt village can clearly be seen on the right side of the frame, yet it isn't mentioned. Later in the movie, we see the same exact village, but this time it's Barnsdale, England, where Robin is from. The village is unharmed, but soon it's burned by Godfrey and his men, revealing to us that it's the same set from the one in France.
Many "cities in the North" are being ransacked and burnt, but Peterborough is not a city in the North of England.
In the beginning of the movie, an army of 3000+ men is left to pillage and plunder in France after Richard dies; nothing is ever made mention again of these men in the movie. Yet the French are able to raise an army to invade England while leaving this other British army behind on French land. Where did this French army come from to be able to invade England?