Continuity mistake: In the elevator scene, when Jack is on top of the elevator, Payne sends the elevator to floor 46 from floor 28, but a second later when Jack looks up at the camera, if you look very closely, you can see he is on floor 15...16...17..., but he's supposed to go up from 28 to 46.
Revealing mistake: In the shot where Jack and Harry are descending a ladder to the stranded elevator, we get a good look at the elevator shaft and its surroundings. Upon closer inspection you'll notice how the lowermost section of the shaft is actually a mural - given away by the shadows cast upon it.
Continuity mistake: When they run onto the roof near the start, there's another trooper behind Harry running onto the roof (only visible in widescreen - in 4:3 it looks like a weird reflection). In the following shot of Keanu Reeves you can see the reflections of Harry and the other guy on the plastic covering the scaffolding. We're led to believe that Harry and Jack should be the only ones up there, as everyone else has a job to do. Aside from those two shots, this third trooper disappears once they start hooking the crane up.
Continuity mistake: When Howard Payne is in the elevator, he hears Jack and Harry doing something from above, and he reaches for his bomb trigger. In slow motion when he's picking it up, it has two buttons on it, yet when Howard pushes one of the buttons, the device now has three.
Factual error: When Payne blows the safety catch on the elevator it shows a shot of the floor level indicator going down from 29 to 25 in about 3 seconds. The camera cuts to inside for 5 seconds then the cable stopping the lift. This has taken approximately 8-10 seconds in total, but they are only on the 22 floor now. By the rate of which they were falling they should be on at least the 13th floor. Not taking into account that it would be accelerating as it goes down.
Continuity mistake: At the beginning of the movie after Jack has hooked up the crane from outside to the lift, there is a shot of the crane outside, and the line going through the vent. If you look closely there is a pipe in front of the vent, yet when the crane goes through the vent, the pipe has vanished.
Continuity mistake: When the crane breaks free from its bolts and starts flying towards some ventilation windows, it obliterates the upper pair. However in the next view from within an air duct, both of these windows just swing open freely as the crane busts through, and yet they barely appear to have suffered a scratch or bend in the process.
Revealing mistake: During the rescue of the elevator passengers at the start of the movie, when coaxing the last woman out, there is a shot of the interior of the elevator where you can see the ground through the hole in the elevator floor, even though the elevator is still meant to be on the 22nd floor.
Continuity mistake: When Dennis Hopper's shooting the shotgun through the lift roof, the number of holes doesn't match the number of blasts. He shoots once and a hole appears. We then see a close up of him and he shoots twice more, but when we cut to the ceiling after the third shot overall, there are only two holes in it. Doesn't seem likely he'd miss the roof at a range of 2 feet.
Continuity mistake: When Dennis Hopper psyches the police chief out by making him think he's on the third floor, the elevator clicks one too many times. The camera shows the numbers: "5, click, 4, click" then it switches to the police chief, during which time you hear another click. It then switches back to the numbers: "3, click." Shouldn't it be on floor 2?
Continuity mistake: In the first part of the movie, it appears that the building is approximately 53 floors high, we can see this as when Keanu Reeves and Jeff Daniels go to the roof the label on the door is "ROOF/53". However, the service elevator seems to reach the top of the shaft after Dennis Hopper enters level 46 on the control panel. This is rather unfortunate, especially as the security console says that the elevator "serves floors GE-52". I wouldn't like to be in the elevator as it tries to go past level 46 to a higher floor such as 52.