Continuity mistake: Arnold goes to the gay bar to solicit the help of the guy he saved at the beginning of the movie. The guy is wearing a white shirt and a vest black/gold lamay. During their conversation he takes off the vest, then it cuts to another bartender. When it cuts back the guy has the vest on, another shot and the vest is off again. (00:08:05 - 01:10:50)
Continuity mistake: Even aside from the ridiculous recoil that a railgun would cause (yeah, I know they don't use gunpowder, but there's got to be SOME opposite movement, surely), how come when the darts (bullets, whatever) go straight through people, they still get thrown backwards? The passage straight through them means minimal energy being transferred to them, and as such they shouldn't be hurled backwards that much.
Continuity mistake: Arnold dives to save the girl under the lid of a fridge. When all the drill bits are shot at him with his hand above the fridge door, none hit his hand. But in the next angle one penetrated his hand. Then in the next scene, when he's driving the van with both hands and when he swipes the credit card the wound appears and disappears. (00:28:30)
Continuity mistake: After the court scene, when Arnold and Vanessa are making their exit toward the van, they get in, the van explodes and the camera pans to the underside of the van, showing Arnold pulling a manhole cover closed. The manhole cover was not there when they showed the van from a distance and they didn't have enough time to get in the van and escape through the bottom. Also, because several seconds passed before he closed the manhole cover you would have to assume he was still above ground when the bomb went off, therefore killing him. (01:46:20)
Visible crew/equipment: When the warehouse has collapsed on Arnold and he is coming out from underneath the rubble, you can see a guy "hidden" behind some tubes, wearing protective eye wear and holding a welding rod to make a shower of sparks (he is only visible in the widescreen DVD version). (01:34:30)