Factual error: The story is carried out during the 14th century (specifically in 1344). In a scene when the group formed by Nicolas Cage and the knights enters in the dark forest of Wormwood, a comparison with a panda bear is given during a fight between the knights. But this is a fatal historical error. Panda bear was discovered in 1869 (525 years later of historical time of the movie).
Continuity mistake: At the end of the fight where the altar boy must prove his fighting skills, the sword changes hands between shots when his hands are up.