Continuity mistake: In the beginning of the movie, when you first see Mary-Kate (aka Mel) and Ashley (aka Ally), Mary-Kate walks off without ever closing her locker.
Other mistake: When Mary-Kate and Ashley arrive at the dance, the two boys are up on stage with their band. They are both playing the guitar, but when they see the twins they put down the guitars and go to see the girls. The thing is that the music sounds exactly the same before they leave as after they leave.
Continuity mistake: When Jean & Michel are playing their guitars on stage with their band. They see Melanie & Ally at the dance, they put down their guitars and go over to them. As the twins are talking to someone else, you can see them in the background pointing to them & getting off the stage again.
Continuity mistake: When the girls are getting out of the car the first time they met Jeremy, Ally's hair was flipped up. Then when they go inside to meet their grandfather her hair is flipped under.
Other mistake: When they are changing Rodin Museum To Luxembourg Gardens, they type in an H, but there aren't any H's in Luxembourg Gardens.
Continuity mistake: When they are passing the note at school with their feet, the teacher talks about Napoleon disappearing from the world stage. Then he says the exact same thing the next day.
Plot hole: When the twins go shopping with Brigitte, you will notice that they go to several different stores and bring the clothes they have not bought outside to try on. Don't you think you'd be arrested if you went outside the shop with a garment on that you have not bought?
Visible crew/equipment: When the girls are going outside to the car with Brigitte to go shopping, a shadow from one of the microphones passes over the car.
Continuity mistake: In the scene where the staff are saying goodbye to Melanie and Ally, Brigitte is wearing one dress. When she comes out of the embassy, she is wearing a completely different dress.
Other mistake: When Mary-Kate and Ashley are jumping and fighting on the bed, listing to music, a pillow falls off the bed, then in the next scene they are still jumping and the pillow was up on the bed again.
Continuity mistake: In the end at the dinner party, they are walking down the stairs and Mary-Kate (Melanie) has one piece of hair sticking out really badly, but in the next shot, her hair is perfectly fine.
Continuity mistake: When they arrive at the mansion Ashley (Ally) starts to take out a brush from her backpack, then in the next scene her bag is closed, then in the scene after that she's taking out the brush again.