Continuity mistake: When Will runs in and takes a photo of Matt Damon and Grace kissing, to get evidence Matt is straight, when Jack pulls out the film from his camera, two boxes (a black and red one) vanish from the coffee table. (01:20:20)
Continuity mistake: When Beverley walks out of his hotel room to talk to Karen, he places a bucket with a champagne bottle in it, on the floor. In the next shot the bottle and white napkin are on the other side of the bucket. (01:15:10)
Continuity mistake: When Matt and Grace are drinking mint tea, when Jack comes into the room to borrow Grace, Grace's mug of tea vanishes from her hand between the shots. (01:17:40)
Visible crew/equipment: As the chorus director says he wants to do the song again because "this Owen Person" didn't show up for his callback, there is a whole boom dipping into view. (00:05:35)