Sounds like a bit of confusion there on Harris' part...
Greg Allman was an Executive Producer on the film, not a line producer. He was involved in the financing and budgets and probably had a contract which included a clause on creative control ( as many will when the film is about them ).
Executive producer
An executive producer (EP) enables the making of a commercial entertainment product. They may be concerned with management accounting and/or with associated legal issues (like copyrights or royalties).[1] An EP generally contributes to the film's budget and may or may not work on set.[2]
Motion Pictures
In Motion Pictures, an executive producer oversees the filmmaking with regard to film finance. They liaise with the line producer and report to production companies and distributors.[3]
Television
In Television, an executive producer often supervises the creative content as well as the financial aspects of a production.
http://en.wikipedia.org/wiki/Executive_producerA line producer is a type of film producer that functions as the key manager during the daily operations of a feature film, television film or the episode of a TV program. A line producer works on one film at a time.[1] He or she is accountable for human resources and all kinds of problems possibly occurring during the making.[2
http://en.wikipedia.org/wiki/Line_producer
