When Meg and Emma meet while out with their respective dates, the Aston is on the right and the scooter on the left. A moment later, when Riley acknowledges the prince, the Aston is on the left and the scooter on the right.
When Grace is given the breakfast order at the beginning of the film the eggs on the plate are crispy and burnt. Yet when she hands the food to the customer the eggs are clearly different from the ones on the plate before.
When Amanda is walking to the podium to give her graduation speech, her graduation robe is open. In the next shot when she starts her speech, it is zipped all the way to the top.
Emma is watching Grace Kelly in To Catch a Thief (1955) in the hotel room in Monte Carlo. When Grace Kelly became the Princess Consort of Monaco all of her films were banned from ever being shown in the country of Monaco, including the capital city Monte Carlo.
The airport stamps that Emma, Meg, Grace and Owen received upon arrival are country exit stamps. The arrow on the stamp should have been pointing to the right upon arrival into a country, not left.
The airport stamps in passports of Meg, Grace and Emma are dated June 19, 2010. The stamp in Owen's passport is from June 22, 2010. However, when Owen arrives to Monte Carlo, he shows the issue of the newspapers from June 10, 2010 featuring Emma, Grace and Meg on the front page.
When checking in at a hotel in a foreign country, the hotel asks for your passport to register you as a guest. This means that the desk clerk at the Hotel in Monte Carlo would instantly know that Selena's character was an impostor.
At the end of the movie, Owen risks electrocuting himself just to please Emma, by installing a dimmer light switch without first turning off the mains power.
When Emma (Katie Cassidy)is walking around the streets of Paris in high heels while on a walking trip,Meg (Leighton Meester)questions her about the practically of her shoes.Emma responds with :"If they [the shoes] ain't hurting,they ain't helping!"Yet all through the movie,Emma is seen carrying her shoes and walking around barefoot ;she frequently kicks off her shoes while in the hotel.It appears her motto should have been :"They are hurting so I'm not wearing them!"