All marriage scenes invariably use the wording of the Book of Common Prayer, which was written in connection with the Reformation several hundreds of years later. In 1194, all clergy would have been Catholic and said the Mass in Latin at weddings.
When Robin and Azeem land on the English coast, there is a shot of a line of white cliffs. These are the Seven Sisters cliffs in East Sussex, England. The Belle Tout lighthouse, built in 1832, is visible on top of the farthest "sister".
When the sheriff notices that a scar has been drawn on his statue, he turns around to two women behind him and tells one of them to come to his room at 10:40, and the other at 10:45. Such precise timekeeping was not kept in 1194, and it would definitely not have been possible for two servants.
Azeem demands Robin tell him which way is East so that he may pray. However, as a Muslim, he would want to know the direction was Qibla (toward Mecca). In England, this would be almost exactly southeast.
When Locksley is writing his letter asking for news of his son, he says "Were you present at his capture near Jerusalem?" but when we see the close up of the letter, it reads, "Were you present at his capture near Acre?"
When Robin and Azeem are mounting the catapult to be launched over the castle walls, Azeem puts his sword in a point down position. In the next cut it's pointing upward. When they are launched over the wall, it is sheathed.
When Robin and Wulf are having a competitive target practice, Wulf's hair is shaggy looking on both sides of his head. But in the close-up of Wulf taking aim, the right side of his hair is slicked back so that Robin can tickle his ear with the feather from the arrow.
When Robin returns to England, the second shot is of the back of the boat that he and Azeem travel in. However, Robin is not visible in the boat until the very next shot, in which he is standing at the front, quite clearly visible.
At the beginning of the movie when Robin is attempting to free the prisoners chained to the wall in the dungeon, Azeem is shown begging to be freed. While pleading his case he rises to his feet and his hands are shown bound in front of him, then the camera goes back to Robin continuing to futilely pull on the chains, showing Azeem in the foreground; then there's a cut to Azeem (apparently sitting, as when he was first shown moments earlier) with his back to the wall and his hands raised and bound on either side of his head yelling "Christian!" to get Robin's attention. A second later he's back on his feet with his hands tied in front of him when Robin runs over and asks why he should save him.
When Robin pretends he is blind and he bends down to rub horse crap on himself, he is wearing black boots with silver studding. When he and Azeem are being catapulted over the wall he is wearing brown lace up boots.
When John Little and Robin first meet at the river, John is seen from the back, holding the staff away from him. "Do you lead this rabble?". In the next shot where John replies "Yes I do, Mate.", the staff is leaned against his shoulder. But in the next shot, the staff is being held away from him again.
As Robin is pulled up the chandelier rope, the end of the rope is close to falling off the pulley. One shot later, the rope is back on the pulley again, with the same length falling as was there before.
When Robin and Azeem are escaping from the sheriff's men at Marian's home, Robin's horse is shot with a crossbow bolt, and as they escape one can clearly see that the arrow is broken since the part sticking out of the horse has no feathers. Later when they stop, right before they enter the Sherwood Forrest, Robin turns to the wound and breaks the arrow, removing the (now reappearing) feathers.
In the battle with the Celts, Little John is fighting on the ground with Robin and Azeem. Yet, in the closing moments of the battle when the archers are driving the Celts off, Little John can be seen up in the trees with the other archers.
When Robin and Azeem "steal" Marion's horses, the Sheriff's men shoot arrows at them as they flee. All the arrows are shown bouncing off the statue to Robin's left as they go out the door, but when they show them riding across the fields, his horse has an arrow embedded on its right flank. They never showed it hitting the horse.
When Robin and Azeem arrive in Dover, Robin says we will be dining with my father by nightfall. Nottingham is over 170 miles from Dover. Robin then makes an extravagant detour via the "Robin Hood" gap in Hadrian's Wall (approximately 120 miles north of Nottingham) before heading south again; making a rather unlikely journey total of more than 400 miles in under a day.
When Robin begins training the outlaws, we see an arrowhead being cast, outdoors in a small mould. Next, we see an iron/steel arrowhead being shaped on a stone. Iron or steel could not be cast, outdoors and in the small quantity as shown, due to the heat needed. The metal shown can only be pewter, lead or tin. To produce arrowheads in those conditions, a friendly blacksmith would beat out a suitably thin piece of waste metal, chop pieces off, then, others could file or rub them to shape and sharpness.
The Sheriff's scribe tells him that Robin and his men have looted money from them for about five months. Assuming that the looting started about the time that Robin slashed the Sheriff's face, his scar shouldn't still be red or still be stitched up.
Toward the end, Azeem is about to shoot a flaming arrow at an explosive barrel. The guard ties a rope around Will's neck and forces him down on to the barrel, and Azeem blows out the flaming arrow. If it were that easy to extinguish the arrow, it never would have stayed lit during fight.
In the battle with the Celts, nearly every Celt who is hit by an arrow and killed is played by stunt coordinator Nick Gillard, who thus dies several times as different characters. If you look carefully you can recognize him.
While rescuing the boy, Robin grabs a crossbow and throws it at one of the soldiers, "hitting" him in the face. The crossbow hits Plexiglas in front of the soldier, and leaves a scratch that is momentarily visible.
After Wulf is saved from the Sheriff's men and runs off, Azeem walks around the rock wall and casts an unnaturally sharp, dark shadow (lighting error), despite having complained about there being "no sun in this cursed country" and it being visibly overcast outside.
When Marian is attacked and taken hostage at her house, Duncan goes to a white horse to find Robin. Several times we see light reflecting in his eyes, but it was mentioned earlier that his eyes were taken in the attack on Locksley Castle.
In the early part of the fight with the Celts, the film is reversed making it appear that Robin is shooting left handed. Obviously done so that Robin was shooting to the left where the Celts were coming from.
During the final fight between Robin and the Sheriff, Marian douses the Sheriff in hot wax. For the next two shots, the Sheriff's shirt is clean. But when we cut back to the fight after the Friar kills the Bishop, the Sheriff's shirt is covered in wax and he has horrible burns on his chest.
When the Sheriff is on top of Marian during their wedding ceremony, he is wearing a black, silver and white striped coat. But in the very next shot, he only has a black shirt on, without showing the coat was removed.
In the extended version, the Sheriff has the scribe's tongue cut out, and the scribe is later shown using writing to communicate. However, at the end of the movie, Robin forces the scribe to tell him where Nottingham and Marion are, and he speaks... without a tongue.
In the climax when Marion, the bishop, the sheriff and the witch are locked in the room, Robin and Azeem are unable to find a way in and start banging on the door. However, without introducing a secret exit from the room, the witch leaves to silence the banging on the door and the bishop leaves as well. Later, the witch magically reenters the chamber so Azeem can burst through the door and kill her.