ERROR: 177: playing sound AVAudioPlayer [Swift]

I'm getting this error message when I play a sound, error has always happened the first time you play the sound, in some tests the error does not appear and in other sim ..

var beep : AVAudioPlayer?

override func viewDidLoad()  {

        super.viewDidLoad()

          if let beep = self.setupAudioPlayerWithFile("beep", type:"wav") {
            self.beep = beep
        }


//SOM
func setupAudioPlayerWithFile(file:NSString, type:NSString) -> AVAudioPlayer?  {
    let path = NSBundle.mainBundle().pathForResource(file as String, ofType: type as String)
    let url = NSURL.fileURLWithPath(path!)

    var audioPlayer:AVAudioPlayer?

    do {
        try audioPlayer = AVAudioPlayer(contentsOfURL: url)
    } catch {
        print("Player not available")
    }

    return audioPlayer
}

//Para tocar
            beep?.play()