Tried to Load Angular More Than Once

This could be a number of issues: essentially it's a problem of routeProvider not finding a file and recursively loading the default.

For me, it turned out that it wasn't minification but concatenation of the js that caused the problems.

angular.module('myApp').config(['$routeProvider', function ($routeProvider) {
    $routeProvider
      .when('/', {
        templateUrl: 'views/listing.html',
        controller: 'ListingCtrl'
      })
      .otherwise({
        redirectTo: '/'
      });
  }]).constant('FIREBASE_URL', 'something');

You'll notice that if the app can't find a file (i.e., otherwise), then it will redirect to the root, which in this case loads the templateUrl. But if your templateUrl is wrong, then it will cause a recursion that reloads index.html loading angular (and everything else) over and over.

In my case, grunt-concat caused the templateUrl to be wrong after build, but not before.

The problem could occur when $templateCacheProvider is trying to resolve a template in the templateCache or through your project directory that does not exist

Example:

templateUrl: 'views/wrongPathToTemplate'

Should be:

templateUrl: 'views/home.html'

This doesn't have anything to do with app.js at all. Instead, this warning is logged when you include the Angular JS library more than once.

I've managed to reproduce the error in this JSBin. Note the two script tags (two different versions):

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.14/angular.min.js"></script>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.15/angular.min.js"></script>

Relevant Angular code at GitHub.