This is the error message received in XCode:
2016-04-24 19:10:59.020 Bumble Bee[7286:421679] *** Terminating app due to uncaught exception 'NSUnknownKeyException', reason: '[<Bumble_Bee.LoginController 0x7fc723db1ee0> setValue:forUndefinedKey:]: this class is not key value coding-compliant for the key LoginTextField.'
The app was working fine until I added a new Swift file and defined a new custom view controller class named "LoginController".