Continuity mistake: In the "playing bars" music montage scene, there is a shot where Fish and Curtis high five. It's a shot from their final concert that hasn't happened yet. Fish's hair is already short.
Factual error: In the scene when ADD is first leaving to go on tour, they drive past the Rock and Roll Hall of Fame and the bus driver announces, "On your left..." The shot of the museum as they drive by is the front. The road going by this way dead ends; there would be no way for them to get on the highway or a surface road. (Look on Google Maps. They are on East 9th Street going northwest.)
Other mistake: In the scene where ADD is playing Rock Band in the tour bus, the game continues to play by itself after Matt, Curtis and Amelia are interrupted by a phone call from their manager informing them that they will shoot a music video.