Corrected entry: In one of the first scenes where the characters wake up, there is a shot where a breakfast cereal's package is seen in the lower left corner of the screen. The brand image of that package is reversed.
Corrected entry: This is a strong contender for the mistake earliest into a movie: When Charles' alarm clock rings at 9.00 the hour hand hasn't reached the set time yet (about 9.30). This happens 7 seconds after the movie actually starts, and it happens again when he gets up for the second wedding. (00:00:35 - 00:33:15)
Corrected entry: After the first wedding, the group is making their way across the lawn towards the receiving line. One shot shows them from behind, and then it cuts to view them from the front. In the scene from behind, David is missing. Matthew can be seen with his arm around Scarlett, but when they switch to the front view, David's arm is around Scarlett, and Matthew is walking ahead of them, with Fiona and Gareth.
Corrected entry: In a scene after the funeral, all the mourners are standing on a dock facing the water - if you look at the water it has little waves in it that do not move (it's a still shot of water).
Corrected entry: When Charles thanks Matthew for being his best man, Matthew apologizes for being late and says "9:45, 45 minutes till I do". This means that Charles is getting married at 10:30. After Fiona wipes lipstick off Charles's cheek, we see a close up of the church clock which reads 10:40. We then see people arriving before it cuts to the priest and Charles inside an empty church. Even allowing for the fact that Charles is always late for weddings and tradition states that the bride should be 20 min. late, surely there would be some people inside the church waiting for the ceremony to begin at 10:30.