When Jane and Roxy are locked in the limo, there is a shot of them from outside the window and they are visible. In the next shot, and throughout the rest of the movie, the limousine windows are tinted.
All through the movie they talk about Jane trying for a scholarship to Oxford. But all the things during the fellowship speech have signs saying "study in London". Oxford university is not in London, it is, rather, in Oxford.
When Simple Plan starts the show, the bass drum head shows a big Drum Workshop "DW" on top of the logo. During the performance, the "DW" is no longer there. As soon as they stop and Eugene Levi dives into the crowd, they flash back to the stage and the "DW" is back
When the twins leap, mosh-pit style, into the crowd, they run towards the crowd, leap and do a half-rotation in midair so that they land on their backs. In the first angle, where they run towards the camera, they rotate in the opposite direction. (At one point their backs are towards each other.) While they are in the air, there is a cut to the reverse angle where we see them leap again. This time they rotate in the same direction so that, at one point, one twin is facing the back of the other.
When Roxy and Jane are in the convenience store and ask to use the bathroom, the employee says it is for paying customers only so she picks up a little Tootsie Roll candy. but when the employee takes it off the counter, it's a piece of Bazooka gum.
When the twins get out of the car, after being chased by Lomax, their hair is a mess. While they are walking, their hair seems to be perfect, just like they got it restyled, and when they start their conversation, their hair is messy again.
The girls are supposed to be from Nassau County on Long Island. When they go to take the train to the city they get on the "Nassau Railroad." There is no such thing. They would have taken the Long Island Rail Road - and the movie's trains look nothing like the LIRR's.
When Trey is locked in the trunk of the car and finally let out (after the trunk was opened) you can see the emergency safety release handle hanging down, which would prevent him from actually being locked in the trunk.
When Max Lomax chases the twins through New York with the big van, at one point the twins think they lost him, but then they find out he's next to them. They turn to the right to look at him, but you can in fact see through the rear window that the van is actually still behind them.