performSegueWithIdentifier for didSelectRowAtIndexPath and IBAction

The code would open the first ViewController and it works fine:

    func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
    self.performSegueWithIdentifier("openDates", sender: self.dates[indexPath.row])
}

override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
    let tasksViewController = segue.destinationViewController as! TasksViewController
    tasksViewController.selectedList = sender as! Dates
}

This code opens the second ViewController but it doesn't work:

    @IBAction func ShowDetails(sender: UIBarButtonItem) {
    self.performSegueWithIdentifier("openDetails", sender: sender)
}

Error message:

Could not cast value of type 'dante.DetailsViewController' (0x10b60b2e0) to 'dante.TasksViewController' (0x10b60adc0).