Fixing ‘Can’t Retrieve Entity Config’ Error in Magento 1.9

i followed this tutorial and got problems with the install script. I get the following error:

Can't retrieve entity config: practice_checkoutcomments/comments

here is the code:

app\etc\modules\Practice_CheckoutComments.xml

    <?xml version="1.0" encoding="UTF-8"?>
<config>
    <modules>
        <Practice_CheckoutComments>
            <active>true</active>
            <codePool>local</codePool>
            <depends>
                <Mage_Sales />
                <Mage_CatalogInventory />
                <Mage_Checkout />
            </depends>
        </Practice_CheckoutComments>
    </modules>
</config>

app\code\local\Practice\CheckoutComments\etc\config.xml

   <?xml version="1.0" encoding="UTF-8"?>
<config>
    <modules>
        <Practice_CheckoutComments>
            <version>0.0.1</version>
        </Practice_CheckoutComments>
    </modules>

    <global>
        <resources>
            <checkoutcomments_setup>
                <setup>
                    <module>Practice_CheckoutComments</module>
                </setup>
            </checkoutcomments_setup>
        </resources>
    </global>
</config>

app\code\local\Practice\CheckoutComments\sql\checkoutcomments_setup\install-0.0.1.php

   <?php
$installer = $this;
$installer->startSetup();

$table = $installer->getConnection()
    ->newTable($installer->getTable('checkoutcomments/comments_table'))
    ->addColumn('comment_id', Varien_Db_Ddl_Table::TYPE_INTEGER, null, 
        array(
                'identity' => true,
                'unsigned' => true,
                'nullable' => false,
                'primary' => true
        ), 'Comment ID')
    ->addColumn('order_id', Varien_Db_Ddl_Table::TYPE_INTEGER, null, 
        array(
                'unsigned' => true,
                'nullable' => false
        ), 'Real Order ID')
    ->addColumn('comment', Varien_Db_Ddl_Table::TYPE_TEXT, '64k', array(), 'Comment')
    ->addForeignKey(
        $installer->getFkName('checkoutcomments/comments_table', 'order_id', 
                'sales/order', 'entity_id'), 'order_id', 
        $installer->getTable('sales/order'), 'entity_id', 
        Varien_Db_Ddl_Table::ACTION_CASCADE, Varien_Db_Ddl_Table::ACTION_CASCADE)
    ->setComment('Checkout Comments');

$installer->getConnection()->createTable($table);
$installer->endSetup();
?>