Errors made by characters (possibly deliberate errors by the filmmakers): When some members of the group are talking about some famous Rock Stars have died, "Outspan" mentions Eliot "Mama" Cass' cause of death as a heart attack. The others correct him by saying it was by choking on her own vomit but it was indeed due to a heart attack.
Factual errors: When listing famous rock stars who died, "the guy from Free" was listed as "died choking on vomit." Paul Kossoff actually died of drug-related heart problems.
Audio/visual unsynchronized: In the last club scene, an acoustic piano can clearly be heard, but only a Fender Rhodes piano is seen.
Factual errors: When "The Commitments" play in their last gig, there is a big brass accompaniment. They are supposed just two. It's best heard during "In the Midnight Hour": there's a tenor saxophone from nowhere playing.