viewDidLoad errors in connection with view controllers

Question

After upgrading to Swift 3, I started getting a BAD INSTRUCTION error every time I clicked a button that was supposed to open a new view controller, relating to the code that's in my ViewDidLoad. Here's the code in my ViewDidLoad:

if teacherModeVar == "Teacher" && password != "No password set" {
        teacherModeRadioButton.state = NSOnState
        singleUserRadioButton.state = NSOffState
        unlockSettingsLabel.isEnabled = true
        unlockSettingsTextBox.isEnabled = true
        unlockSettingsButton.isEnabled = true
        levelChoiceLabel.isEnabled = false
        levelChoiceHelp.isEnabled = false
        levelChoiceOption.isEnabled = false
        teacherPasswordLabel.isEnabled = false
        teacherPasswordHelp.isEnabled = false
        enterNewPasswordLabel.isEnabled = false
        enterNewPasswordBox.isEnabled = false
        confirmPasswordLabel.isEnabled = false
        confirmPasswordBox.isEnabled = false
        saveNewPasswordButton.isEnabled = false
        typeOfLearnerLabel.isEnabled = false
        typeOfLearnerOption.isEnabled = false
    } else {
        teacherModeRadioButton.state = NSOnState
        singleUserRadioButton.state = NSOffState
        unlockSettingsLabel.isEnabled = false
        unlockSettingsTextBox.isEnabled = false
        unlockSettingsButton.isEnabled = false
        levelChoiceLabel.isEnabled = true
        levelChoiceHelp.isEnabled = true
        levelChoiceOption.isEnabled = true
        teacherPasswordLabel.isEnabled = true
        teacherPasswordHelp.isEnabled = true
        enterNewPasswordLabel.isEnabled = true
        enterNewPasswordBox.isEnabled = true
        confirmPasswordLabel.isEnabled = true
        confirmPasswordBox.isEnabled = true
        saveNewPasswordButton.isEnabled = true
        typeOfLearnerLabel.isEnabled = false
        typeOfLearnerOption.isEnabled = false
    }
    if teacherModeVar == "Single" {
        singleUserRadioButton.state = NSOnState
        teacherModeRadioButton.state = NSOffState
        unlockSettingsLabel.isEnabled = false
        unlockSettingsTextBox.isEnabled = false
        unlockSettingsButton.isEnabled = false
        levelChoiceLabel.isEnabled = false
        levelChoiceHelp.isEnabled = false
        levelChoiceOption.isEnabled = false
        teacherPasswordLabel.isEnabled = false
        teacherPasswordHelp.isEnabled = false
        enterNewPasswordLabel.isEnabled = false
        enterNewPasswordBox.isEnabled = false
        confirmPasswordLabel.isEnabled = false
        confirmPasswordBox.isEnabled = false
        saveNewPasswordButton.isEnabled = false
        typeOfLearnerLabel.isEnabled = true
        typeOfLearnerOption.isEnabled = true

I'm basically using NSUserDefaults to populate the Preferences area correctly. It was working fine in Swift 2/Xcode 7, but after updating to Swift 3/Xcode 8 it gives me trouble. Any thoughts or ideas would be appreciated!