I am new in magento and creating a module for use of both frontend and backend. Module works perfectly on frontend but it does not work in Magento Admin. It goes to **404** page.Here is the config file and `IndexController` file. Any help?

**config.xml** 

```
<config>
<modules>
    <Mymodule_Customerpage>
        <version>1.0.0</version>
    </Mymodule_Customerpage>
</modules>
<admin>
    <routers>
        <the_name_of_this_element_is_not_important_it_should_be_unique>
            <use>admin</use>
            <args>
                <modules>
                <Mymodule_Customerpage before="Mage_Adminhtml">Mymodule_Customerpage</Mymodule_Customerpage>
                </modules>
            </args>
        </the_name_of_this_element_is_not_important_it_should_be_unique>
    </routers>
</admin>
<adminhtml>
    <menu>
        <tutorial_menu translate="title" module="mymodule_customerpage">
            <title>Artwork</title> 
            <sort_order>9999</sort_order>
            <children>
                <first_page module="mymodule_customerpage">
                    <title>Artwork</title> 
                    <action>adminhtml/mymodule_customerpage/index</action>
                </first_page>
            </children>
        </tutorial_menu>
    </menu>    
</adminhtml>
<frontend>
    <layout>
        <updates>
            <mymodule_customerpage module="mymodule_customerpage">
                <file>mymodule_customerpage.xml</file>
            </mymodule_customerpage>
        </updates>
    </layout>    
    <routers>
        <mymodule_customerpage>
            <use>standard</use>
            <args>
                <module>Mymodule_Customerpage</module>
                <frontName>mymodule_customerpage</frontName>
            </args>
        </mymodule_customerpage>
    </routers>        
</frontend>
<global>
<models>
    <mymodule_customerpage>
        <class>Mymodule_Customerpage_Model</class>
        <resourceModel>mymodule_customerpage_mysql4</resourceModel>
    </mymodule_customerpage>
    <mymodule_customerpage_mysql4>
        <class>Mymodule_Customerpage_Model_Mysql4</class>
        <entities>
            <customerpage>
                <table>customerpage</table>
            </customerpage>
        </entities>
    </mymodule_customerpage_mysql4>
</models>
<resources>
    <mymodule_customerpage_setup>
        <setup>
            <module>Mymodule_Customerpage</module>
        </setup>
        <connection>
            <use>core_setup</use>
        </connection>
    </mymodule_customerpage_setup>
    <mymodule_customerpage_write>
        <connection>
            <use>core_write</use>
        </connection>
    </mymodule_customerpage_write>
    <mymodule_customerpage_read>
        <connection>
            <use>core_read</use>
        </connection>
    </mymodule_customerpage_read>
</resources>
<helpers>
    <mymodule_customerpage>
        <class>Mymodule_Customerpage_Helper</class>
    </mymodule_customerpage>
</helpers>

```

*Mymodule/Customerpage/Controller/Adminhtml/IndexController.php*

```
class Mymodule_Customerpage_Adminhtml_IndexController extends Mage_Adminhtml_Controller_Action{
public function indexAction()
{
    $this->loadLayout();

     $block = $this->getLayout()
     ->createBlock('core/text', 'adminhtml_artwork')
     ->setText('<h1>This is a text block</h1>');

    $this->_addContent($block);

    $this->renderLayout();
} }

```