Factual error: When the Ranger trainees first meet Samuel L. Jackson, he's wearing the rank of a Specialist on his collars even though he's a Master Sergeant. Title 18, Chapter 33 of the US code prevents the unauthorized wear of a military uniform (among other things), however this does not automatically correct the mistake since a common misconception is that one slight alteration is sufficient to make the uniform legal. Having the wrong rank on is too obvious of an alteration, especially for anybody who has spent more than a day in or around the Army and would still be punishable by law, if he was dressed in an attempt to fool your average citizen outside of a movie.
Factual error: There is one scene in the movie where Heath Ledger reads a Latin sentence in a book. As he is translating the sentence, he goes over the words one by one with his finger. This would never be possible in a Latin sentence, because words in Latin are never - I repeat: never - in exactly the same order as in English. Words that actually belong together can be placed on opposite ends of a sentence.
Factual error: In the scene where Meg Ryan and her sister are in the coffee shop, her sister calls to the waitress that they ordered a latte, no foam, very dry - it is impossible to make a dry latte without foam, because dry means "foamy." Not to mention, a very dry latte is technically a cappuccino.
Factual error: When the zombies are about to over-run the house, one of the ravers sacrifices himself by shooting a keg of gunpowder to blow up the building. The problem is that gunpowder is not an impact explosive, you could shoot that keg all day and all it would do is put holes in it. Just shooting it would not cause an explosion.
Factual error: The prisoner is described as carrying an "Axis IV Dissociative Disorder"; that is complete nonsense - dissociative disorders are placed on Axis I in psychiatric diagnoses (Axis I is clinically treatable disorders; Axis II is mental retardation/personality disorders; Axis III is concomitant health problems (e.g., hypertension, diabetes mellitus, CABG, etc.); Axis IV is a list of psychosocial stressors and their severity (e.g., "Moderate - Health problems, financial problems"); Axis V is the GAF score (Global Assessment of Function, scored from 0 - 100). *Any* clinical professional with psychiatric experience would put dissociative disorder on Axis I except for the psychiatrist in the film, who apparently doesn't know any better. (00:54:00)