Other mistake: At the end of the movie, when Cory is in Natalie's bedroom, Cory stops and looks at a picture of Natalie and his daughter wearing a high school graduation cap and gown. Cory said his daughter was only 16 when she died so she would've already been dead by the time Natalie graduated. (01:36:00)
Other mistake: Introducing the workplace to the new employee (Banderas), Vance says that the mall has never been updated because it has everything "Menswear, kidswear, ladieswear, cosmetics." The Italian dub misinterprets the last word (probably figuring it was 'medics'), and so the mall has the rather unlikely lineup; "Menswear, kidswear, ladieswear, doctors." (00:14:20)
Other mistake: The private investigator has a full size Glock. The Glock 21 which is a .45 ACP has the lowest magazine capacity of 13 rounds. The 9mm capacity for the Glock 17 is 17 rounds. The PI exchanges gun fire and after he fires 7 rounds, his gun runs dry. Makes no sense to bring a half empty gun to a fight, plus he just got it back from his brother-in-law. (01:05:00 - 01:06:00)
Other mistake: Henry and Peter got on the school bus in the morning and Susan picked them up after school. Parents often drive their kids to/from school, even when busses are available. Busses usually aren't available for students within short walking distances to school. The day Peter looked "lost" when school let out, Christina walked him home. This indicates the school is close - close enough that Susan wouldn't need to speed to home and back during the talent show or take 45 minutes to execute the plan. (00:02:48 - 00:51:39)
Other mistake: When Harry Hole gets a call but isn't there to answer, Katrine Bratt picks up the phone and takes a message. Rebecca from Telenor Security tell her they picked up a cellphone signal from a missing person. She tells her the coordinates as Parkway 1, 0139 Oslo. On Katrine Bratt's computer you see the coordinates as Parkway 1, 0350 Oslo. (01:13:15)
Other mistake: During the opening trap we see Mitch strike the blades with his chain and get yanked forward. However, despite being yanked forward he still manages to stand in line with the others which he shouldn't be able to do, as his chain was shorter due to the extra tug he received. (00:06:30)
Other mistake: The phone wire was cut in the boy's room when he called his uncle. Yet his uncle used the same phone to make a call just before he died.