Factual error: The movie takes place during the 1990s, but throughout the movie cars are shown with Illinois license plates with "Illinois" written in cursive. These plates were not introduced until 2001. (00:24:45)
Continuity mistake: When the house first becomes detaches from its foundation and becomes airborne, Russell is nowhere to be seen, although every angle of the house is shown, including underneath, the front porch and the back porch. He knocks on the door and tells Carl he chased a "snipe" under the porch - but he cannot be seen after liftoff and prior to knocking. The same thing happens near the end, when Dug claims to have hidden under the porch.
Continuity mistake: When Paul Blart puts on his Hello Kitty bandaid on his arm in the next shot it has disappeared.
Character mistake: When the two main characters are approached by the coach in the school, they make a bet on how many times the coach will say sh*t, the coach says it 9 times, but Nick says that there were ten.
Continuity mistake: After Mike and Ned fight with lightsabers, when they are in the kitchen Mike's wedding ring moves from his left hand to his right hand and back again, depending on the angle of the shot. (00:21:05)
Continuity mistake: During the sequence where Margaret proposes to Andrew on the street in New York, the same woman in a green sweater walks by three times.
Continuity mistake: When Grumpy jumps the chasm to chase Dr. Marshall, there's a large green bulbous plant that moves from the side Grumpy jumped from to the one he lands on. It wasn't there before.
Continuity mistake: In the scene where Stu, Phil, and Allan are retrieving the tiger back to Mike Tyson, the tiger scratches Phil. As they get out of the car, the camera has the tiger in full frame as he growls at Phil, you see chains around the tigers' neck as a leash that was never there before.
Character mistake: About 3/4 of the way through the movie, when Jennifer Aniston is talking to Ben Affleck, she calls him Ben instead of his character's name Neil.
Visible crew/equipment: During Lilly's sweet 16 party at Santa Monica Pier, when she is skateboarding and catches hold of Drew, in the two shots facing Lilly the reflector screen and boom mic are reflected on the helmet to Drew's left. (00:14:00)
Continuity mistake: After the car chase, the front plate of the taxi is hanging on one side. Moments later, while driving the cab and fighting the other "alien," the plate on the taxi is in a different position (semi-fixed). (00:46:00)
Continuity mistake: When Ian films the Chipettes during the sing-off, he says, "If you like what you see then call Ian Hawke." But when someone else plays the video back later, he says, "If you're interested, then call Ian Hawke."
Continuity mistake: While being held by the two kidnappers, both Neal and Mellissa go from being handcuffed together to being handcuffed individually, and then back to being handcuffed to each other once again.
Revealing mistake: After Martin cuts his arm off, there are several scenes where you can see the bulge of the actor's real arm under his jacket. This is most noticeable when he is running through the birch wood, and when rooting through the ruins of the burned cabin.
Visible crew/equipment: In the scene with Darth Vader and Oscar the Grouch, watch Darth Vader's eyes. You can see the light screens and crew reflected in his eyes in every shot.
Character mistake: When Mr Maddens is talking to the critic at the Mayor's reception, he calls him Alan. The character is actually called Patrick Burns, Alan is the actor's name.
Other mistake: After Bruno and Lutz had been arrested and are outside the police station arguing, in the background in the left corner, there is a gold Ford Mustang. Then as Lutz is walking away, the same gold Ford Mustang is seen driving in to park in that same place.
Visible crew/equipment: When Emma goes to crash Liv's wedding ceremony, as she crashes through the glass doors you can see film crew reflected in the glass panes.
Continuity mistake: In the dream scene where Larry writes on the blackboard in front of the student audience, when Larry writes on the blackboard he writes the wrong formula "delta p = square root of <p>^2 - <p>^2". The bell rings, the students leave and you see Larry again in a close-up and above his shoulder you see the the first 2-squared moves from outside the bracket into the bracket. (01:06:35)
Visible crew/equipment: At the start of the scene where Evan is racing to the school to get to the choir, you see some buildings. If you look down when the angle is turning to the right, it focuses on some cranes, a camera, and a wire holding it up, and a crew member is visible in the reflection of a red window.