Script problems are the reason given for the delay in the Jack Ryan project (Ryan, of course, is created by Tom Clancy and made his first appearance on screen in Hunt For Red October).
Says Deadline, "The slow process of nailing the Ryan script has prompted the studio to focus on getting Pine at the helm of the USS Enterprise first, even as the studio waits to see if JJ Abrams will reprise as Trek director.... Paramount's expectation is for the Star Trek sequel to start production by the fall so that the studio can keep that film's projected June 29, 2012 release date. Alex Kurtzman, Roberto Orci and Damon Lindelof are are working on the script."
For more on the Jack Ryan situation, follow the link.