Continuity: Near the end of the movie, Scully's white Ford Taurus is parked outside, even though it had been wrecked earlier in the film. When Scully comes out of the house, a silver Ford Fusion is parked outside.
Factual errors: In the film, they refer to the Richmond "DA" who appears later. Virginia has no District Attorneys. Prosecutors in Virginia are Commonwealth's Attorneys.
Errors in geography: Though the attacks occur in Somerset, West Virginia, in one scene shot from inside the victim's car, you can clearly see a Virginia State Police Inspection sticker.
Continuity: While driving on a snow-covered road, Mulder collides with a truck equipped with a snow plow. His car's front headlight is visibly damaged. In the next scenes, the damage changes from shot to shot.
Factual errors: Scully and Mulder fly in on a helicopter from their house. After landing and exiting the helicopter the rotor is still turning but Scully's and Mulder's hair remain in place. The rotor wash would blow their hair around, in the next shot you see them walking away from helicopter with the rotor still turning.
Errors in geography: In parts of the movie, you can clearly see snow capped mountains in the background. No such mountains exist in West Virginia.
Continuity: Dacyshyn abducts his second victim of the movie by sideswiping her car with his snow plow. When Mulder trails him later in the movie, there is no damage to Dacyshyn's vehicle.