The fake pass used by Modell is seen being written in cursive with a pen, but when he enters Holly's room, it's written in all caps with a thick marker.
In real life, the FBI Headquarters is guarded by the FBI Police force. However, in the episode, it is being shown as being guarded by private security guards.
Even in 1996, it would have taken more than a few seconds for the FBI to have traced the phone number of someone calling from an insecure phone.
When the FBI HRT member is shown trying to light himself on fire using a Zippo lighter, it's implied that he would need to generate an actual flame to ignite the gasoline that he was forced to drench himself with beforehand. In reality, mere sparks from the lighter would more than enough to light off the gasoline or its vapors.
Furthering a previous error, both Mulder and Scully's ID cards read: US Department of Investigation, Federal Bureau of Justice. The words Investigation and Justice have been switched.
The FBI motto on the building is incorrect as it reads "UNITED STATES BUREAU OF INVESTIGATION" instead of "FEDERAL BUREAU OF INVESTIGATION".
When at the golf driving range, the establishing shots show Pusher and his friends driving off in bright sunshine while the scenes at the rear of the range - when Collins lights himself on fire - show rain on the ground and piles of snow.
Fox Mulder is an experienced FBI agent who seemingly has years of experience handling firearms and firing them at gun ranges. Yet he is showing both blinking and flinching when he fires his service weapon which he would have to know would impair his accuracy.
When Mulder inspects the cans of Mango and Kiwi Tropical Swirl in the refrigerator, he incorrectly calls out "Hey Scully, check this out: Mango and Kiwi Tropical Squirrel".