CANNES - Not everyone is enamoured with Robert Rodriguez's ultra-violent movie 'Sin City,' based on the dark comics of Frank Miller, but the creators are working on a sequel and the cast of stars is keen to carry on. The film, which has earned more than $72 million at the U.S. box office alone, is in Cannes as part of the main competition, raising eyebrows among veteran festival-watchers who are used to more artistic, less commercial fare.