Mistakes
At the end, there's a white car parked outside Mulder and Scully's house. When Scully comes out, it's now a silver car. See more...
Movie Mistakes blog
Popular blog posts:
Top 15 biggest Harry Potter film mistakes
30 Biggest mistakes in the Star Wars movies
The 10 biggest mistakes in Iron Man 1 & 2
Other great sites
The X-Files: I Want to Believe (2008) - 2 trivia entries
starring David Duchovny, Gillian Anderson, Mitch Pileggi (add more)