Factual error: He uses an AmEx platinum card at the Nikko Hotel, but the number starts with 3713. Platinum cards all start with 372.
Plot hole: When Nick confronts the P.I. and yells "Why are you following me?", he looks inside the car and see the file with his picture on the front seat. The P.I. notices this and turns the file over. After Nick grabs his gun, the P.I. jumps out on the other side, raises his hands in the air and tells him someone hired him and runs off. As the P.I. runs off, Nick yells "Who hired you?" as he stands alone next to the car. He then waits a minute and walks off. If he really wanted to know more information, he could have taken the file that was right in front of him on the carseat. It makes no sense that he is desperate for information about the strange events that are going on, sees this file on him, and yet doesn't even pick it up or look at it. (00:59:55)
Plot hole: At the end, when Nick is on the roof and everyone is behind the metal doors, you hear the saws trying cut through the door and the sparks flying. Immediately when they cut through, the doors swing open and everyone is standing right up front with Champagne glasses. No one is holding any saws or equipment or have any in front of them. Nor was there any time for the people cutting the doors to run to the back to hide behind everyone else since the sparks fly right up until the doors swing wide open. (01:53:40)
Continuity mistake: In the scene at the restaurant, when the waitress runs into Michael Douglas and they both get wine all over each other, watch her shirt carefully. In one shot there are many wine stains all over. The next shot, there's not much. Then it goes back to having lots of wine stains. (00:35:40)
Deliberate mistake: Every time Nicholas enters his gate at home, it's daylight and then when he drives up to the house it is night. Either he has a 300 mile property or there is something else going on. It would appear that it is deliberate as it happens many times in the film. Symbolically, Nick is leaving the world as he appears with wealth and privilege (light) and entering the real van Orton world of solitude and sadness (dark). (00:09:00 - 00:09:55)
Continuity mistake: When Nick is being followed by the PI, watch the chase car carefully. Several times both seats in the PI's car are occupied yet when Nick confronts him, the PI is alone. (00:58:55 - 00:59:45)
Revealing mistake: When Nick is being followed by the PI, several times Nick's speedometer is seen to be at zero. (00:58:40)
Continuity mistake: When Nick confronts the old man in the hotel after he sees the pictures, he throws them in the old man's lap. Watch the cup and one of the pictures jump around between shots. Sometimes the cup is gone and the picture moves. (01:01:05 - 01:02:00)
Other mistake: After taking the CRS test, while talking with Feingold, Nicholas corrects his use of "unsatisfied" with "dissatisfied". Feingold responds, "That's right, you're a left-brain word fetishist." But earlier, on the phone with his ex-wife, Nicholas describes her growing family as "nucular" (as opposed to "nuclear" - the "cl" sound in the middle is key). Someone obsessive about word use would never make this mistake, it is classically seen as a sign of low intelligence and/or backward education. (00:11:55 - 00:19:50)
Audio problem: When the ambulance goes to the hospital and the people disappear and he answers, "I'm sorry about that," you can see clearly that his lips don't actually move. (00:40:15)
Audio problem: When Michael Douglas catches up with James Rebhorn at the zoo, just as Douglas grabs Rebhorn he pulls him in close and brandishes his pistol. You hear the sound of the gun being cocked (i.e. the hammer being pulled back), but when the camera actually shows the gun, the hammer is not in the cocked position. (01:43:10)
Character mistake: When Nicolas returns from Mexico and goes to the gate of his house, he sees a sign that says his house is being sold at public auction. The word "foreclosure" is spelled incorrectly. It is spelled "forclosure."