Really great advise, except that the SAME error CAN occur simply by missing the critical script include on your root page
example:
page: index.html
np-app="saleApp"
Missing
<script src="./ordersController.js"></script>
When a Route is told what controller and view to serve up:
.when('/orders/:customerId', {
controller: 'OrdersController',
templateUrl: 'views/orders.html'
})
So essential the undefined controller issue CAN occur in this accidental mistake of not even referencing the controller!