Factual error: In the background the full moon is visible and it's early morning (approx. 6:00 AM). However, at the start of the episode we see the full moon at night (approx. 19:50). Due to the fact that these are consecutive days, this situation is impossible from an astronomic point of view.
Factual error: The last number on the truck's license plate is "77." On Russian plates the last two/three digits stand for a registration place. "77" is a number for Moscow, but the Gulag is located in Krasnoyarsk region, so the number should be different. Besides, the format of the plate (LDDDDL|DD) is incorrect - the correct one is LDDDLL|DD (L - letter, D - digit).
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.
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.
Continuity mistake: Clyde Bruckman commits suicide by placing a plastic bag over his head until he asphyxiates. However, when Mulder and Scully first discover him you can see in the shot just before Scully holds his hands that there is no plastic bag around his head (may only be visible in widescreen format).