Casting error using BWWWalkthroughController in Swift for iOS

I'm trying to create a regular walkthrough for my iOS app using the open source BWWWalkthroughController framework (link: https://github.com/ariok/BWWalkthrough ), but I can't get it to work!

Here's the class where the error occurs:

import UIKit

class StartPageViewController: UIViewController, BWWalkthroughViewControllerDelegate {

override func viewDidLoad() {
    super.viewDidLoad()
}

override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)

    let userDefaults = NSUserDefaults.standardUserDefaults()

    if !userDefaults.boolForKey("walkthroughPresented") {

        showWalkthrough()

        userDefaults.setBool(true, forKey: "walkthroughPresented")
        userDefaults.synchronize()
    }
}

override func didReceiveMemoryWarning() {
    super.didReceiveMemoryWarning()
}

@IBAction func showWalkthrough(){

    // Get view controllers and build the walkthrough
    let stb = UIStoryboard(name: "Walkthrough", bundle: nil)

      

        
        
        
      

    

let walkthrough = stb.instantiateViewControllerWithIdentifier ("walk") how! BWWalkthroughViewController <----- THIS IS WHERE ERROR TO VIEW

    let page_zero = stb.instantiateViewControllerWithIdentifier("walk0") as! UIViewController
    let page_one = stb.instantiateViewControllerWithIdentifier("walk1") as! UIViewController
    let page_two = stb.instantiateViewControllerWithIdentifier("walk2")as! UIViewController

    // Attach the pages to the master
    walkthrough.delegate = self
    walkthrough.addViewController(page_one)
    walkthrough.addViewController(page_two)
    walkthrough.addViewController(page_zero)

    self.presentViewController(walkthrough, animated: true, completion: nil)
}


// MARK: - Walkthrough delegate -

func walkthroughPageDidChange(pageNumber: Int) {
    println("Current Page \(pageNumber)")
}

func walkthroughCloseButtonPressed() {
    self.dismissViewControllerAnimated(true, completion: nil)
}

}

      

        
        
        
      

    

Here's my mistake:

2015-06-29 00:24:02.951 Up & Down - Minimalistic, Beautiful Counter[13041:715011] Unknown class _TtC43Up & Down - Minimalistic, Beautiful Counter27BWWalkthroughViewController in Interface Builder file.
Could not cast value of type 'UIViewController' (0x10570c418) to 'Up___Down___Minimalistic__Beautiful_Counter.BWWalkthroughViewController' (0x103972fb0).
(lldb) 

      

        
        
        
      

    

I have made sure that all classes are named correctly in IB and I am sure everything is connected correctly (outputs, actions, etc.) (I have looked at many similar questions, no answers working for me. Any ideas what the problem is ? THANK!