Continuity mistake: As King Arthur addresses the Knights of the Round Table he says, "Only the Grail can restore leaf and flower" and Perceval and the other nights are facing him. In the next shot Perceval and the knight to the left of him are facing forward with only their heads turned towards Arthur. (01:35:30)
Continuity mistake: King Arthur asks Merlin where evil is in his kingdom and he replies, "Always where you never expect it, always". In the next shot Morgana walks back to her seat at the table as Gawain blurts out, "I know where" but then two shots later we see her back at the wall where she was speaking to Merlin. (01:10:20)
Continuity mistake: As Morgana and Merlin speak, the position of the vial that she's wearing changes between shots. In the shots where we see Merlin's face a gold spec (many are included as decorations in the veil) is next to her cheek. In the shots where we see Morgana's face the gold spec moves and is next to her right temple. (01:01:45)
Continuity mistake: King Arthur's second horseman carries three extra jousting sticks as they ride to the far end of the field preparing for the joust. After the first charge Lancelot says, "You joust well, Sir, I offer you another lance" and King Arthur rides back to his second horseman who now only has one jousting stick. (00:48:15)
Continuity mistake: During the knight's feast at the round table Morgana and Merlin go off to chat and he says to her, "I've shown you too much already". We see three dogs (one lying down and two standing) bathed in a green light behind his head. Two seconds later we see this spot again and there are two dogs standing in natural light. (01:09:30)
Continuity mistake: Morgana becomes old after she recites "The Charm of Making". They use another older actress to portray her and she's wearing the same costume and head dress but they neglected to put on the long dangling earrings that she was wearing in the previous shots when she was younger. (02:07:00)
Continuity mistake: When Arthur is dying after killing Mordred, he drops to his knees with the spear still through him. When Sir Percivle is next to him getting his last instructions, the spear is gone.