During the time period of the movie the matchlock would have been the common firearm, however, the telltale puff of smoke from the flash pan is missing every time one is fired.
The seat on which King Louis XI (Robert Morley) sits in his throne room is not a Gothic throne in 14th Century style, it's a gilt chair in the Rococo style of the late 17th/early 18th Century.
Although the story is set in 1465, the Château de Chambord in Loir-et-Cher, which serves as the Duke of Burgundy's residence, was built between 1519 and 1547. The Château de Maintenon in Eure-et-Loir, which began construction in the 12th Century, was expanded and renovated several times and did not reach the state in which it appears in the film until the 18th Century.
The suit of armour worn by de Creville (Marius Goring) is 16th Century, not 15th Century, in style.
The firearms that seem common in the movie had only recently been developed in the Ottoman empire (Turkey), estimated at the date of this movie 1465, and not found in Europe, especially in quantity as depicted in the move, until around 1475. Nor do these movie firearms closely resemble the long-barreled arquebus, later developed into the matchlock by 1500.