Factual error: When Skinner is at Kritschgau's apartment building, the time stamp onscreen says it's 5:05 AM, but when Kritschgau answers his door, he says it's 6:00 in the morning. Plus it is shown to be broad daylight outside. The sun is never up that early in Washington, D.C.
Continuity mistake: Malcolm Wiggins stabs Alfred Fellig in the back three times, including once in the middle of his back to the right of his spine. However, when Scully is examining Fellig's back later in the episode, he has at least six stab wounds, and all of them are around his shoulder blades.
Visible crew/equipment: When Mulder is driving away from the gas station, crew members as well as some filming equipment can be seen reflected in the car's body. Mulder is in a pretty desolate area, so seeing people reflected in the car's body would in all likelihood be crew members and not random citizens.
Revealing mistake: When Mulder - whilst trapped in the body of Morris Fletcher - is doing various poses in front of the mirror, several of his movements and the corresponding movements from the realized reflection of Morris Fletcher are slightly out of sync with each other.
Add timeSerious B
Continuity mistake: Just as Mulder and Scully are entering the interrogation room to question Lauren for the second time, Mulder is holding a thin stack of paper, folded in half in his right hand. In one shot, these are folded horizontally. In the immediate next shot, they are now folded vertically.
Visible crew/equipment: As the camera flies over the train, in the upper right corner of the screen there is some equipment and umbrella visible that are not likely to just be in the middle of nowhere - probably filming equipment. In the next shot they are gone.