Factual error: When we first see Caine (Bacon) enter the military base, there are Willy's Jeeps used by military personnel. By the year 2000, the Willy's Jeep was long-since replaced in the U.S. Military by the HUMVEE, which we also see in the film.
Revealing mistake: Sebastian Caine wears a latex mask and latex gloves in order to appear near-human. The mask he wears is fairly long, and covers his neck, and the tops of his shoulders and collarbone. However, there is a scene in which Linda and Matt are helping a nauseous Sebastian reach the toilet, where he vomits (invisible fluid) into it. In this scene, when Sebastian breaks free from them and runs to the toilet, we can see that his arms and chest are also visible, skin-colored. The mask he wears only reaches the very base of his neck, so it is possible that the actor playing the invisible man did not realize that the tops of his arms and chest were visible. (00:49:20)
Continuity mistake: When the team tries to make Caine invisible, he tears off all the sensors and wires from his chest. Yet the surrounding machines continue to display his heart rate and blood pressure.
Continuity mistake: When Sebastian goes to Linda's apartment to catch her and Matthew together, we see Linda welcome Matt by pulling her jeans down. Matt picks her up, hands on her bare butt. After he carries her into the bedroom, Sebastian throws a rock through the window and we see them on the bed, her jeans are pulled back up to her waist. Not the direction clothing usually goes in such situations.
Factual error: You see the serum flow toward the heart and then branch out through the rest of the body. The same thing happens when they try to do it with Kevin Bacon. In ANY normal circulatory system, blood that reaches the heart from the veins has to go straight to the lungs to be deoxygenated before it gets sent to the rest of the blood. The serum clearly doesn't do this - the only way that anything could skip the lungs so blatantly is if there was a hole in the heart.
Continuity mistake: When Linda and Matt are trying to escape from the freezer, the amount of blood changes on the door lock.
Continuity mistake: Matt is bitten by the gorilla on his hand in the beginning, but in the next scene where the gorilla is strapped to the table, his hand is fine. Shortly after the gorilla is made visible, his hand is suddenly bandaged.
Visible crew/equipment: When Sebastian is stalking his neighbor and looking at her to see if he can see her undress in the beginning, there is a brief moment where you can see the reflection of a camera crew in the window looking into Sebastian's apartment.
Continuity mistake: In the early part of the movie when Sebastian is checking the stability of the molecule, you see the 3D molecule model explode and the separated atoms pause. When Sebastian turns away, you can see that the atoms are no longer on the same position.
Plot hole: After Sebastian, who is visible by being soaked in blood, kills Sarah, the remaining scientists enter the room and find her body in the freezer in only a short space of time. Sebastian then suddenly surprises and attacks them with no blood on him whatsoever. So in that short amount of time, Sebastian was able to leave the room, sneak past past his colleagues without alerting them, find a shower to wash the blood off him, return to the room and move Sarah's corpse in the freezer, and still had time to wait for the others' arrival.
Other mistake: When the subject is invisible, and the crew are attempting to return it to normal, when they inject the orange anti-serum into both the gorilla's and Caine's bloodstreams, it makes a noticeable "slooshing" noise as it rushes through their veins, which, technically, should make no noise at all.
Continuity mistake: The "tranquilliser guns" are really PGP paintball pistols. The little tube on top only has a little hole the size of a paintball you load it, yet in the movie they seem to hold a good amount of large darts in that tiny gun.