类ORM的对象无法转换为字符串

I´ve one error idiorm, but I don´t know if could be the date?

$insertOrder = ORM::for_table('pedido')->create();
        $insertOrder->fechapedido = date('Y/m/d');
        $insertOrder->estado = 1;
        $insertOrder->empleado_id = $idempleado;
        $insertOrder->proveedor_id =  $_SESSION['idproveedor'];
        $insertOrder->save();

Message: Object of class ORM could not be converted to string File: C:\wamp\www\viver\vendor\j4mie\idiorm\idiorm.php Line: 413

the line 413 is:

  protected static function _execute($query, $parameters = array(), $connection_name = self::DEFAULT_CONNECTION) {
            self::_log_query($query, $parameters, $connection_name);
            $statement = self::$_db[$connection_name]->prepare($query);

            self::$_last_statement = $statement;

            return $statement->execute($parameters);
        }

I´m using an ORM what´s idiorm, used object