为什么我的ajax上出现错误500（内部服务器错误）？

Question

当我尝试将数据用于服务器时问题就开始了。一旦我取消注释这一行$data_product = $this->item->addProduct($descripcion,$cost_price,$selling_price,$wprice,$stock);我得到问题500内部服务器错误，但我不知道为什么如果我有一切正常，ids，名称等我想将我的数组发送到服务器。我该如何调试此错误并修复它？我试过去查看我的日志，但没有任何内容......

这是链接：http://alasksoft.tk/inventory/product 登录凭据：admin - admin

控制器

public function addProduct(){
        $descripcion = $this->input->post('description');
        $cost_price =  $this->input->post('cost_price');
        $selling_price = $this->input->post('selling_price');
        $wprice = $this->input->post('wprice');
        $stock = $this->input->post('stock');
        $data_product = $this->item->addProduct($descripcion,$cost_price,$selling_price,$wprice,$stock);
        $data = array(
            'description' => $descripcion,
            'cost_price' => $cost_price,
            'selling_price' => $selling_price,
            'wprice' => $wprice,
            'stock' => $stock
        );
        $this->json($data_product);
    }

模型

public function addProduct($descripcion,$cost_price,$selling_price,$wprice,$stock){
        $data = array(
            'descripcion' => $descripcion,
            'precio_compra' => $cost_price,
            'precio_venta' => $selling_price,
            'precio_mayoreo' => $wprice,
            'existencia' => $stock
        );

        $query = $this->db->insert('storelte_articulos',$data);
        return $query->result_array();
    }

AJAX

$('#add').on('click',function(){
        $("#description").mask("(999) 999-9999");
        $("#new_product").validate();
        BootstrapDialog.show({
            message: function(dialog) { 
                var $message = $('<div></div>');
                var pageToLoad = dialog.getData('pageToLoad');
                $message.load(pageToLoad);

                return $message;
            },
            data: {
                'pageToLoad': URL_GET_VIEW_PRODUCT
            },
            closable: false,
            buttons:[{
                id: 'btn-ok',
                cssClass: 'btn-primary',
                icon: 'glyphicon glyphicon-send',
                label: ' Save',
                action: function (e) {
                    var description = $('#description').val();
                    var cost_price = $('#cost_price').val();
                    var selling_price = $('#selling_price').val();
                    var wprice = $('#wprice').val();
                    var stock = $('#stock').val();
                    if($("#new_product").valid()){
                        $.ajax({
                            url: URL_GET_ADD_PRODUCT,
                            type: 'POST',
                            data: {description: description, cost_price: cost_price, selling_price: selling_price, wprice: wprice, stock: stock}
                        }).done(function (e) {
                            console.log(e);
                        });
                    }
                }
            },{
                id: 'btn-cancel',
                cssClass: 'btn-danger',
                icon: 'glyphicon glyphicon-remove',
                label: ' Cancel',
                action: function (e) {
                    e.close();
                }
            }]
        });
    });