Factual error: In the North of the Border scene when McClane's helicopter makes an emergency landing you can see a Giant Food trailer in the background. They are supposed to be in Canada, but this grocery store chain is located in the Mid-Atlantic states. This scene was actually filmed in Jessup, MD where Giant has its headquarters.
Visible crew/equipment: There is a shot towards the end of the film, (just before Willis and Jackson exchange dialogue in the engine room) in which it shows the entourage of people boarding a smaller boat from the much larger ship. Look towards the bottom left corner of the screen as the boat pulls away - inside you can see the head of a female boom mike operator.
Revealing mistake: When fighting with Targo on the boat, McClane pulls a chain, which trips Targo over. When we see Targo being tripped from above, you can see it is a stunt double - not only is he bigger than the actor playing Targo, but also his hair is grey unlike Targo's brown.
Continuity mistake: When Bruce Willis swerves into Central Park, he pulls the steering wheel hard left, but the next shot shows the car turning right.
Factual error: The entire plot is based on the idea that they're going to steal $140 billion worth of gold. At a gold price of $300/ounce, that's 14,500 tonnes of gold - how's the suspension on those dump trucks? There's no way trucks like those could carry over 1,000 tonnes each, yet Simon tells McClain there is $13 billion worth of gold in the back of McClain's truck.
Factual error: When the collected bad guys are at the "North of the Border" truck stop, a subtitled henchman tells Jeremy Irons that the helicopter will be ready in ten minutes. But the confused fellow actually says, "...in zwanzig minuten," which means TWENTY minutes!
Factual error: When Zeus goes to Yankee Stadium, the terrorists tell him to report to the home-team dugout. Yet when Zeus goes to Yankee Stadium, he is shown at the dugout along the third-base line, which any Yankee fan knows is the visitor's dugout. Given he knew which dugout he was meant to go to, and the importance of the situation, this can't just be a character mistake.
Revealing mistake: When Willis is driving through the park, you can see the tyre marks and lines where they had driven there on other takes.
Continuity mistake: When the two heroes are crashing through the city in the taxi, the car takes a significant beating. The bumper is pushed up from rough landings and there are long scrapes down each side. When Zeus skids to a halt outside Wall Street station the taxi is in almost perfect condition.
Factual error: When Bruce Willis and Samuel L. Jackson are in the minivan with the feds, the bad guy rings up. This call is taken on an old Motorola flip phone. They plug it into something to make it hands free loud speaker. The thing they plug it into is actually the house charger that comes with the phone, it doesn't have a loud speaker and it's also mains voltage. You can even see the spare battery in the second slot at the back of the charger and the red LED flashing to indicate that the battery is charging.
Continuity mistake: When they first start with the gold operation, Targo jumps on a large orange vehicle with some kind of drill on the front, already raised into the vertical position. He then jumps off and in the very next shot the drill raises from a horizontal to vertical position.
Deliberate mistake: While most of the German spoken in the movie is correct (even if with bad accent) there is a translation error in the scene at Yankee Stadium. When the guy with the sniper rifle gets nervous and asks if he should shoot or not, the other one says,"Nein, wir brauchen den anderen", which would translate, "No, we need the other one", but the subtitles say,"We'll follow him", which they do.
Continuity mistake: When McClane is thrown out of the aqueduct he jumps into the Mercedes driven by Zeus. Then another car shoots at them and they're in a fight. If you look at it closely, the front window of Zeus' Mercedes is broken, but in the next scene it is like nothing happened.
Other mistake: After McClane hits Targo with the chain and knocks him out, McClane searches him. Targo's body is not only in a different position, but the chain is wrapped around his head, which McClane never did.