Magento Observer already exists error

Question

I'm, trying to define and implement observers to catch comments on the checkout page and write them into the database. But when I want to place an order I get the following exception:

Mage registry key "_singleton/checkoutcomments/observer" already exists

Do I get this error because the model is not called properly?

Here is my code:

The config.xml of the module

<frontend>
    <layout>
        <updates>
            <checkoutcomments>
                <file>practice/checkoutcomments.xml</file>
            </checkoutcomments>
        </updates>
    </layout>

    <events>
        <controller_action_predispatch_checkout_onepage_saveOrder>
            <observers>
                <save_checkout_comments>
                    <class>checkoutcomments/observer</class>
                    <method>prepareCheckoutComment</method>
                </save_checkout_comments>
            </observers>
        </controller_action_predispatch_checkout_onepage_saveOrder>

        <sales_order_place_after>
            <observers>
                <save_checkout_comments>
                    <class>checkoutcomments/observer</class>
                    <method>saveCheckoutComment</method>
                </save_checkout_comments>
            </observers>
        </sales_order_place_after>
    </events>

</frontend>

My Observer.php

    <?php

class Practice_CheckoutComments_Model_Observer
{

    public function prepareCheckoutComment ($observer)
    {
        $message = $observer->getControllerAction()
            ->getRequest()
            ->getPost('checkoutcomments');
        Mage::getSingleton('core/session')->setCheckoutComment($message);
    }

    public function saveCheckoutComment ($observer)
    {
        $order = $observer->getOrder();
        $message = Mage::getSingleton('core/session')->getCheckoutComment(true);

        if (!$order || empty($message)) {
            return;
        }

        $commentModel = Mage::getModel('checkoutcomments/comment');
        $commentModel->setOrderId($order->getId())
            ->setComment($message)
            ->save();
    }
}

?>

Answer 1

The observer name of every observer has to be unique. So at least one of the save_checkout_comments tags has to go. I normally use the module name + event so in your case that would be

<controller_action_predispatch_checkout_onepage_saveOrder>
    <observers>
        <checkoutcomments_controller_action_predispatch_checkout_onepage_saveOrder>
        <class>checkoutcomments/observer</class>
        <method>prepareCheckoutComment</method>
        </checkoutcomments_controller_action_predispatch_checkout_onepage_saveOrder>
    </observers>
</controller_action_predispatch_checkout_onepage_saveOrder>

<sales_order_place_after>
    <observers>
        <checkoutcomments_sales_order_place_after>
        <class>checkoutcomments/observer</class>
        <method>saveCheckoutComment</method>
        </checkoutcomments_sales_order_place_after>
    </observers>
</sales_order_place_after>