Continuity mistake: In the scene just before the final attack on the castle, D'Artangan is surrounded by his fellow Musketeers. He gets off his horse and while doing so there is a tight close up where you see clearly that he is wearing his Musketeer outfit that he threw down on the floor in the previous scene. When he finishes talking to the horse (and he is back in his normal clothes) Porthos hands him the Musketeer uniform, which D'Artangan then puts on. (01:20:45)
Continuity mistake: While the character Mena Savari plays is in the credits as Constance, she is referred to as Francesca many times throughtout the movie. In fact, I can't recall a single time she is referred to as Constance.