Problems with adding new tab to customer view in magento backend
===

I'm very new to Magento and I'm trying to add a new tab to the customer view of Magento backend.

I have made a new extension/module for it. Here are some extracts of my etc/config.xml:

    <global>
		<blocks>
            <showidea>
                <class>Whatever_Extendcustomer_Block</class>
            </showidea>
        </blocks>
        <!-- ... -->
    </global>
    <adminhtml>
        <layout>
            <updates>
                <showidea>
                    <file>whatever_extendcustomer.xml</file>
                </showidea>
            </updates>
        </layout>
    </adminhtml>

And here the contents of the whatever_extendcustomer.xml file:

    <adminhtml_customer_edit>
        <reference name="customer_edit_tabs">
            <action method="addTab">
				<name>extendcustomer_showidea</name>
				<block>extendcustomer/adminhtml_customer_showidea</block>
			</action>
        </reference>
    </adminhtml_customer_edit>

Of course this block is existing and it extends the **Mage_Adminhtml_Block_Template** and implements **Mage_Adminhtml_Block_Widget_Tab_Interface**.

When I go to details of a customer I get now the error: Wrong tab configuration.
In Magento's error log stands:

> exception 'Mage_Core_Exception' with message 'Invalid Blocktype:
> Mage_Extendcustomer_Block_Adminhtml_Customer_Showidea' in
> /var/www/vhosts/whatever/htdocs/app/Mage.php:594

And I think this is the problem, because Mage_Extendcustomer is wrong. It should be Whatever_ ... but I don't know why it is prepending the Mage_ instead of my Whatever_ namespace.

I hope someone can give me the clue!
Thanks.