Other mistake: When the girls are chatting on a blanket outside the "haunted" castle, you can see Geri discreetly mouthing other people's lines, particularly Emma's.
Other mistake: In one of the first scenes where the girls are in the recording studio singing "Say You'll Be There" study carefully what each of them are wearing. I.E. Mel B is wearing a space suit. Later in the movie, when they're in Milan, they are all seen wearing the same things.