Early in the movie, there is a montage surrounding the members of the Steel Dragon tribute band driving and singing. A city scene is quickly flashed that shows cars taking off from a red light. The cars in this scene are clearly '90s era vehicles. The most noticeable is the 1994 electric blue Chevy S-10.
After the news conference announcing Chris as the new Steel Dragon lead singer, and Kurt's comments about eating p****, Chris says to his girlfriend "What was I going to do? I can't argue with him." His lips do not at all match what we hear.
As Izzy and Emily are being led through Kurt Cuddy's mansion they momentarily get sidetracked amongst Steel Dragon concert and historical memorabilia. At one point they both stare in utter amazement at a Korina wood Gibson Flying V where Izzy comments, in awed hushed tones, that the fretboard is made of rosewood. The problem with this scenario is the fact that more than 95% of ALL guitars and basses made worldwide have rosewood fretboards, as they are the industry standard. While a small number of guitars do have fretboards made of maple or rare tone-woods such as bubinga, most any working musician, as Izzy supposed to depict, knows that rosewood is by far the most common material used for this feature.
During the scene where Izzy is showing the rest of Steel Dragon his artwork and song ideas for the album, Kirk and A.C. mention that they write ALL the bands songs. Earlier in the film when Izzy is auditioning, its noted that Bobby (the member of the band who was kicked out that Izzy was replacing) wrote one of the bands songs, "Stand Up", about a lover of his. However, it's not much of a stretch to believe that when Bobby was still in the band he was a songwriter himself. When he left, that left Kirk & A.C. as the creative team in the group and Kirk could just have been egotistically conveying that to Izzy.
The movie poster shows Wahlberg with a guitar case strapped to his back, and when he leaves the band and is hitchhiking home he is seen with a guitar, but his character is never seen playing the guitar in the entire movie (before, during or after joining Steel Dragon).
When the member of Steel Dragon leans out the window to shoot the sign that says "Wichita 35 mi" there are mountains visible in the background. There are NO mountains within 300 miles of Wichita let alone 35 miles away.
A few times in the film, the terms "cover band" is used with Chris immediately correcting them that he was in a Steel Dragon tribute band. "Tribute band" and "cover band" are actually different. Chris' band Blood Pollution and their rivals, Black Babylon are "tribute bands" as they cover songs by just one band--Steel Dragon. "Cover bands" on the other hand, cover songs by an assortment of bands and artists, not just sticking to one.
In the Batman vs. Magnum PI drag race scene, Izzy is driving the Batmobile and Kirk Cuddy is driving a Ferrari Mondial. However, the Magnum character did not drive a Mondial, he drove a Ferrari 308 GTS.
After Izzy falls down the stairs, his head is bleeding. He walks backstage after the first song, wipes nearly all the blood off his face. Back onstage 2 seconds later, and he has blood all over his forehead and face. This is NOT a goof, due to the scalp being highly vascular, and thus bleeds profusely from any cut.
After Wahlberg leaves Steel Dragon, he hitchhikes home. He has been playing with Steel Dragon for approximately 1 year at this point and would have earned a lot of money. There is no reason for him to have to hitchhike home - he owns the 60s Batmobile. Even if he wanted to give up all of the fame and fortune of his rock star ways, he could have easily used some of his money to buy a bus ticket at the very least.
On the tour bus, AC offers Izzy something that he says is good for writing lyrics. Later on, Kirk tells Izzy he and A.C. do all the writing. Why offer him something that's good for writing lyrics if AC and Kirk do all the writing? A.C. might just have temporarily forgotten that rule or might just have lied to Chris to make him feel more welcome as a new member of the band or Kirk hadn't informed A.C. that Chris wasn't going to be allowed to contribute any music to the band.