500（内部服务器错误）symfony jquery ajax

Question

我收到的错误消息如下：

jquery.min.js:6 POST http://localhost:8000/etl/ 500 (Internal Server Error)send @ jquery.min.js:6ajax @ jquery.min.js:6(anonymous function) @ (index):763dispatch @ jquery.js:5087elemData.handle @ jquery.js:4895ListPicker._handleMouseUp @ about:blank:550
jquery.min.js:6 XHR finished loading: POST "http://localhost:8000/etl/".send @ jquery.min.js:6ajax @ jquery.min.js:6(anonymous function) @ (index):763dispatch @ jquery.js:5087elemData.handle @ jquery.js:4895ListPicker._handleMouseUp @ about:blank:550

昨天的代码工作得很好。我不知道哪里出了问题。

JS代码：

            <script>
                var $outTable = $('#etl_outTable');
                $outTable.change(function() {
                    $('#etl_outField').attr("disabled",true);
                    var $form = $(this).closest('form');
                var data = {};
                data[$outTable.attr('name')] = $outTable.val();
                $.ajax({
                    url : $form.attr('action'),
                    type: $form.attr('method'),
                    data : data,
                    success: function(html) {
                        // Replace current position field ...
                        $('#etl_outField').replaceWith(
                                // ... with the returned one from the AJAX response.
                                $(html).find('#etl_outField')
                        );
                        $('#etl_outField').attr("disabled",false);
                    }
                });
            });
        </script>

我在做http://symfony.com/doc/current/cookbook/form/dynamic_form_modification.html#dynamic-generation-for-submitted-forms 希望得到一些帮助！谢谢！