Dawson Casting: Drew Barrymore was 23 when she played the 18-year-old Danielle.
Dougray Scott (who was 33) as well. Given that Prince Henry was meant to be only a few years older than Danielle (perhaps anywhere between 20-25) it's a rather bizarre casting choice.
Fake Nationality: The movie has French people being played by people from the US (Drew Barrymore, Anjelica Huston), Scotland (Dougray Scott), New Zealand (Melanie Lynskey) and England (most of the rest of the cast) - capped by most of them speaking with English accents, even if they're not playing someone French (like the actor cast as Leonardo da Vinci). Averted by actual Gallic actress Jeanne Moreau as the Famous Ancestor (if not by French actor Christian Marc... as the King of Spain!).