Continuity mistake: During the first fight scene in the castle, the fourth guard to die charges through the castle door and is killed by Robin Hood. The shot cuts and the guard is immediately followed by Sir Guy, but in between those two shots an arrow suddenly appears in the door which wasn't there before.
Revealing mistake: In the big fight scene at the end, there is a close-up shot of a guard (Sir Mortimer) getting stabbed square in the chest. When the sword is withdrawn, there is no hole in his tunic.
Continuity mistake: During the first fight the fourth guard Robin Hood kills is the one who charges through the castle door. This guard is shot right in the heart causing him to clutch were the arrow is protruding from his heart as he dies with first his left hand and then his right hand on top of his left after he drops his sword. He then fall forwards, his body coming to rest face down, still clutching the arrow with both hands after it becomes still. But in the next scene his body is laying on his back facing up he is still clutching the arrow with his right hand but his left hand is laying by his side. Even if one of other guards had rolled him over it should have been his right hand that would have fallen off first, because it was on top of his left hand.
Suggested correction: No car, just light on the hilt of Scarlett's sword.
I verified the scene. It's definitely not from the light of Scarlett's sword. It occurs after Will gets off his horse and the horse is turning. To the right of the horse is a tree in the background. To the right of that is a small clearing, about level with the horse's mouth. For a fraction of a second you can see a white object go across the small clearing in the same manner as a white car driving by.
Bishop73