Plot hole: When Renee Russo was reviewing the tape showing the room with the painting to see who stole the painting, and the tape was blank because the heat generated from the suitcase hidden under the bench, why didn't she just back up the tape completely to see who put the suitcase there in the first place? (00:28:30)
Plot hole: Catherine Zeta Jones says that she needs ten extra seconds after midnight to download the program that collects the billions of dollars from the international bank. In the movie at two different point, she states that after 11:00 PM the device she linked to the clock is gathering an extra 1/10 of a second every minute to allow for ten seconds at midnight. If you take a tenth of a second a minute for 60 minutes, you end up with only 6 seconds. 4 seconds short of the required 10. Some people say she only says "a fraction", but she explains the scenario twice. In one instance, she indeed says a fraction, the other time she definitely says 1/10th of a second, which is wrong.
Plot hole: When Henry rings Maurice's doorbell to give the bad news about Sarah's fatal illness, Maurice and Sarah are upstairs in the bedroom. Maurice approaches the window and looks down while we see Henry looking up in his direction. That he walks away without trying to make contact makes no sense. (01:13:45)
Plot hole: There are a few references in the movie about Cory, Peggy, Cousin Cindy, Maggie, etc. growing up together in Hale, Maryland (East coast). Why, then, does Peggy have an obvious Midwest accent? (I know 'Peggy' talks like this in real life; in the movie it seems out of place next to the other characters, who all sound the same).
Plot hole: After Hugh Grant visits Julia Roberts in the Ritz Hotel, he is seen entering a bus to return to his flat. The camera pans back to reveal her photo on the rear of the bus, forgetting that the bus is heading east down Piccadilly, and away from Notting Hill.