When Sydney dives from the balcony into the hotel pool, the stolen necklace is not around her ankle. When she's in the water, it is.
Marshall writes Michael Vaughn's height in his fake criminal record as 1.60 meters 60 inches. Michael Vartan is 1.83 meters, and is clearly taller in the picture shown than Jennifer Garner, who is 1.73 meters. Also, 60 inches = 1.524 meters.
The Spaniard characters talk in Latin American accents.
To make clear that Sloan is in Zurich a title card is show. Problem is that the title card is show over a shot of Amsterdam.
Perez's man phones the Spanish police to alert of a "robero" at the hotel. The actual Spanish word for robbery is "robo".
While posing as a hotel maid, Sydney uses the words "servicio nocturno de cuarto" to mean "night room service". The right term is "servicio nocturno de habitaciones".