Class AppDelegate: UIResponder, UIApplicationDelegate ERROR

#1

Everything runs pretty well until the last code before the challenges. As soon as I built and run the app and try to switch between the map views the app stops responding and I get an error in the AppDelegate.swift file

import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate     //ERROR HERE

Any ideas what I am doing wrong?

#2

// ERROR HERE does not provide useful clues.

What is the actual error you are getting?