AngularJS Error

I got this error in inspector:

Error: [ngRepeat:dupes] http://errors.angularjs.org/1.2.9/ngRepeat/dupes?p0=subject%20in%20subjects&p1=string%3A%D0%90%D1%81%D1%82%D1%80%D0%BE%D0%BD%D0%BE%D0%BC%D0%B8%D1%8F
    at Error (<anonymous>)
    at http://vedomosti/js/angular.min.js:6:449
    at http://vedomosti/js/angular.min.js:184:445
    at Object.fn (http://vedomosti/js/angular.min.js:99:371)
    at h.$digest (http://vedomosti/js/angular.min.js:100:299)
    at h.$apply (http://vedomosti/js/angular.min.js:103:100)
    at f (http://vedomosti/js/angular.min.js:67:98)
    at E (http://vedomosti/js/angular.min.js:71:85)
    at XMLHttpRequest.v.onreadystatechange (http://vedomosti/js/angular.min.js:72:133) angular.min.js:84

But I don't understand where my mistake...

I'm writing an application for school. I have table school in MySQL. With fields: id, name, 1,2,3,4,5,6,7,8,9,10,11

1,2,3,4... it's classes and they are have information about subjects. Each class have their subjects. Now I'm writing part, in which user can set subjects into classes. 1 to 10 classes all works good. But when I click "load subjects from 11 class", I get this error.

This table with subjects:

div class="large-6 column">
                <label>Предметы {{class}} класса</label>
                <table>
                    <thead>
                    <tr>
                        <th style="width: 200px;">Предмет</th>
                        <th style="width: 200px;">Изменить</th>
                    </tr>
                    </thead>
                    <tbody>
                    <tr ng-repeat="subject in subjects">
                        <td>{{subject}}</td>
                        <td><a>изменить</a></td>
                    </tr>
                    </tbody>
                </table>
            </div>

And button for load information other classes:

<button class="button success tiny" ng-click="getSCLASS()">получить</button>

And function for this button:

$scope.getSCLASS = function(){
        $http.post("/index.php/panel/getSCLASS", {class:$scope.class}).success(function(data){
            $scope.subjects = data;
            $scope.s_subjects = true;

        });
    }

From 1 to 10 classes - all works good. But with 11 class it's not work. I don't understand where my mistake.

Sorry for my English :|