Factual error: Every time the silver nitrate is shown on clothing, it is shown as silver. Silver nitrate in fact is black once exposed to light.
Continuity mistake: At the end when the 3 vampires are shooting at Michael, Selene drops behind them. The blood on the left side of her head disappears and reappears a couple of times. When she's taken them out it's back again. And it gets bigger and smaller all during the time it's there.
Audio problem: Near the beginning of the movie, while Selene is looking at the CCTV video from outside the subway station, Kraven enters the room and talks to her. Throughout their conversation, the sound quality of his voice changes as he walks away from where the mic is located (by Selene).
Continuity mistake: When Lucian goes flying over Selene's car, in the overhead shot we see that the road below him has large parts with visible concrete because there are no paving stones. But in the next shot, a close-up of Lucian landing on his feet, the road is fully paved with paving stones.
Revealing mistake: When Selene is firing her guns in the floor making a circle of holes so that the floor collapse, you can see in some shots the angle of her guns are pointing all kinds of directions. Instead of making a perfect circle the holes would be spread around the floor and the bottom of the walls in the hallway.
Continuity mistake: At the shooting range, Selene is shown firing a black USP without a compensator. It then cuts to an over the shoulder shot, and she is now firing a two-tone USP Match (which she supposedly receives from Kahn to test out a few seconds later). It then cuts to a frontal shot of her, and she is once again using the same black USP. She never stopped firing, so she couldn't have switched guns.
Revealing mistake: After Selene jumps off the building at the beginning and lands, there is a very large upwards pull (that stays in place until the camera cuts away) in her cape near her head that is in fact the drop wire running under her cape to the harness on her back (although the wire has been edited out).