Help! I don't know why my app keeps crashing.

//PlaylistMasterViewController 

import UIKit

class PlaylistMasterViewController: UIViewController {

    @IBOutlet weak var buttonPressLabel: UIButton!

    override func viewDidLoad() {
        super.viewDidLoad()

    buttonPressLabel.setTitle("Press Me", forState: .Normal)


    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.

    }

    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        if segue.identifier == "showPlaylistDetail" {
            let playlistDetailController = segue.destinationViewController as
                PlaylistDetailViewController
            playlistDetailController.segueLabelText = "Yay you pressed the button"

        }

    }

}

//PlaylistDetailViewController 

import UIKit

class PlaylistDetailViewController: UIViewController {

    @IBOutlet weak var aButton: UILabel!
    var segueLabelText: String = ""


    override func viewDidLoad() {
        super.viewDidLoad()

        aButton.text = segueLabelText

    }

    override func didReceiveMemoryWarning() {
        super.didReceiveMemoryWarning()
        // Dispose of any resources that can be recreated.
    }

}