The shots of the McFly concert in Times Square were actually shot in England for McFly's home-fan base. While changing lighting and camera angles, McFly would play their other songs for the fans before playing the ones for the movie while filming.
While everyone else would rehearse for a scene, Lindsay Lohan would sit in a corner and a stand-in would do her scene with the other principal actors. Then, when film rolled, Lohan would saunter over and repeatedly flub her lines after which she'd often throw a fit and someone had to console her and lead her away.
The film was meant to be a starring vehicle for Lindsay Lohan to transition from family fare to adult roles. Its resounding commercial failure and well-publicized production woes centered around Lohan's unprofessional behind-the-scenes behavior marked the beginning of her career downfall.
For filming the concert scenes in England, fans were told when booking the tickets that they could be in the filming for this movie. This was so that they wouldn't bring any merchandise or banners, to coincide with the idea that McFly were an undiscovered band.
While filming was ongoing in New Orleans, local newspaper The Times-Picayune published a long article detailing the hard-partying, nightlife-loving ways of co-stars Lindsay Lohan and Samaire Armstrong and its negative effects on the production, pondering whether this would have an impact on Lohan's career, as she was at the time one of the most in-demand actresses in Hollywood.