NEW YORK — Producers of Paul Simon’s “The Capeman” have postponed the musical’s Broadway opening by three weeks to give the creative team time to fix some problems. The $11 million musical, previously set to open Jan. 8, now will open Jan. 29.Rumors of a troubled production have been circulating in the Broadway community for weeks, and renowned stage directors Mike Nichols and Nicholas Hytner recently attended previews to offer notes for improvements. The production, which did not have an out-of-town tryout, is being directed by dance innovator (and stage musical novice) Mark Morris. Insiders say the producers (Klores, Plenaro Prods., Brad Grey and Edgar Dobie) generally are happy with Simon’s music, but Morris’ staging and the book (by Simon and Derek Walcott) is too slow. A statement released by the producers Tuesday said the postponement will “allow more time to rehearse and introduce new material into the show” and provide 65 hours of additional rehearsal time. A spokesman for the show said producers do not plan to replace Morris, but declined further comment. “The Capeman” is based on a the true story of Salvador Agron, a Puerto Rican boy who, at 16, was sentenced to death (later commuted) for the gang-related slayings of two Hell’s Kitchen teenagers. Agron was dubbed the Capeman by New York City tabloids because of the vampire-style cape he wore. Previews, which began Dec. 1 at the Marquis Theater, will continue until the Jan. 29 opening, with preview prices ($55-$67.50) in effect until then. Top prices jump to $75 after opening.