Continuity mistake: Kevin Kline is walking through a vineyard. His shoes change from boots to loafers in the same scene.
Continuity mistake: In the restaurant at Cannes, Meg Ryan stumbles backward over a dessert cart and lands with her face clearly on the floor. After a cutaway to the diners' reacting to the crash, Meg's face is squarely in a chocolate cake. Maybe she just became hungry after the accident.
Continuity mistake: When Kate comes out of the bathroom after taking her shower in Cannes, she has thick eye shadow on. That's some shower she's had...
Suggested correction: Her hair is also dry and styled. It's obvious that she did her hair and makeup before leaving the bathroom.
Continuity mistake: Kate is speaking to Charlie on the phone when he says he's met a woman. The length of the wire changes from short to very long instantly.
Continuity mistake: When Meg Ryan and Kevin Kline are having breakfast in the train, the label on the water bottle changes position between shots.
Continuity mistake: When Kate and Luc are chatting in the plane, a shot from the outside shows the man behind sleeping, with his face turned towards the window, but the next shot, inside, shows his head facing straight forward.