When Marie and Philippe are kissing on the couch, the dog on the couch disappears and reappears a couple of times.
Christina is supposed to be the princess of Belgium. The intertitles constantly remind us that the year is 1789. The Kingdom of Belgium did not exist before 1830.
When the duchess and the peasant woman give birth, the children are placed in a mismatch fashion. The Doctor places the twins together correctly when he attempts to mismatch them.
When Mimi is on the wheel in the dungeon, her dress doesn't move as she is spinning. It should fall over her head when she is upside down.
Twentieth century buses visible on a bridge in background of swordfight.
The Man in the Iron Mask was arrested and imprisoned over a hundred years before the events of this film.