Factual error: The film takes place in 1981 (the film very specifically states that it takes place "EXACTLY 500 years" after the prologue set in 1481), meaning that the several references to the Nintendo Entertainment System don't make sense, since they weren't released until a few years later, in the mid-80's. ('83 in Japan under the name "Famicom" and 1985 in North America to be exact).
Visible crew/equipment: As Bruce Willis and Andi McDowell improbably make their castle-escape aboard the da Vinci glider, a wide, open-air aerial shot looking down shows the model glider pass right through the shadow of the hovering helicopter that is shooting the footage.