Continuity mistake: When Wayne and Garth are on their way to the Alice Cooper concert they show the car from behind you can clearly see that Garth is driving and Wayne is in the passenger seat but when they cut back to the car from inside Wayne is driving and Garth is in the passenger seat. (00:56:50)
Plot hole: When Wayne and Garth are trying to get Mr Big to hear Cassandra's band, they refer to when they spoke to the security guard earlier in the movie. They claim he said Mr Big would be in Chicago on Friday when he actually didn't - he never mentioned a specific day at all and just said he was travelling that way next week. (00:59:50 - 01:12:40)
Continuity mistake: When Wayne, Garth, Cassandra and Benjamin are at Benjamin's apartment, The level of Cassandra's champagne when she is standing out on the balcony is low. Cassandra then walks inside and sits on the sofa, where the level of champagne in her glass is higher, without anyone giving her a refill. (this is from a video viewing)
Audio problem: Near the end of the movie when the band is playing the song for the guy in the limo when shes singing the chorus to the song the voice changes from the original song to her voice.