Ambiguous use of 'numberOfPages'

I don't understand what is ambiguous about my use of book.numberOfPages in my TableViewController. I'm not having any problems with using any of the other attributes. There shouldn't be any ambiguity here: I have defined it as a Float in the data model editor and at the top of the TableViewController.

 override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
            if segue.identifier == "showBookDetail" {
                let indexPath:NSIndexPath = self.tableView.indexPathForSelectedRow()!
                let book: AnyObject = addBookViewController.fetchedResultsController.objectAtIndexPath(indexPath) as! Book
                var detailViewController:BookDetailViewController = segue.destinationViewController as! BookDetailViewController
                detailViewController.title = book.name
                detailViewController.pagesReadText = "\(Int(book.pagesRead))"
                detailViewController.timeReadText = "\(Int(book.timeRead))"
                println(book.numberOfPages)
            }
        }