Is is possible to make order state to processing from complete programmatically?

Question

i'm try to make a order's state to processing from complete. here is the code

class TempName_HelloWorld_IndexController extends Mage_Core_Controller_Front_Action
{
    public function indexAction()
    {
     $this->loadLayout(array('default'));
     $this->renderLayout();

     $order = Mage::getModel('sales/order');
     $order->loadByIncrementId(100000041);
     $order->setState(Mage_Sales_Model_Order::STATE_PROCESSING, true, 'Gateway has authorized the payment.');
     $order->save();
    }
}

?>

the above code can update the order state from pending/pending payment to processing, but i can't update the order state from complete to processing. Anyone can what is the problem?