According to Britain's Times Online, the problem is, it seems he's leaving his stage role in The History Boys at the National Theatre before his contract is over. They note a spokesperson for the National Theatre said yesterday, Ben Barnes has decided to leave The History Boys early, before his contract is finished. It is something we are taking very seriously. He has accepted an offer to be in a children's Disney film and we have had to fly Jamie King back at extremely short notice this week."
Jamie King will replace Barnes in The History Boys production; The Chronicles of Narnia: Prince Caspian starts production later this month.
The Chronicles of Narnia: Prince Caspian was released May 16th, 2008 and stars Ben Barnes, Georgie Henley, Skandar Keynes, William Moseley, Anna Popplewell, Sergio Castellitto, Peter Dinklage, Warwick Davis. The film is directed by Andrew Adamson.