error to add custom attributes

I am on a site magento 1.7.0.2

I created a module to add an attribute in the customer account. At first it worked, my field has been added and then I realized that I had made a spelling mistake.

so I deleted directly attribute from phpmyadmin.

And when I relaunched the website I get this error when I go to customer management:

Fatal error: Call to a member function getBackend() on a non-object

I tried many things but I have found no solution.

Here are my files :

$installer = $this;


$installer->startSetup();

$this->addAttribute('customer', 'demande', array(
    'type' => 'int', // varchar, text, int, static, datetime
    'input' => 'boolean', // text, select, date
    'label' => 'Demande de compte professionnel',
    'global' => 1,
    'visible' => 1,
    'required' => 0,
    'user_defined' => 1,
    'visible_on_front' => 1
));


/**
 * Si attribut de type select :
 * 'type' => 'select',
 * 'source' => 'eav/entity_attribute_source_table',
 * 'option' => array('values' => array('Mon Option 1', 'Mon Option 2')),
 */

Mage::getSingleton('eav/config')
    ->getAttribute('customer', 'demande')
    ->setData('used_in_forms', array('adminhtml_customer', 'customer_account_create', 'customer_account_edit', 'checkout_register'))
    ->save();


$installer->endSetup();

my config.xml file :

 <admin>
    <routers>
        <customfield>
            <use>admin</use>
            <args>
                <module>Digitgold_Demande</module>
                <frontName>customfield</frontName>
            </args>
        </customfield>
    </routers>
</admin>

<global>
    <fieldsets>
        <customer_account>
             <demande><create>1</create><update>1</update><name>1</name></demande>
        </customer_account>
    </fieldsets>
</global>
<global>
    <resources>
        <customfield_setup>
            <setup>
                <module>Digitgold_Customer</module>
                <class>Mage_Customer_Model_Entity_Setup</class>
            </setup>
            <connection>
                <use>core_setup</use>
            </connection>
        </customfield_setup>
        <customfield_write>
            <connection>
                <use>core_write</use>
            </connection>
        </customfield_write>
        <customfield_read>
            <connection>
                <use>core_read</use>
            </connection>
        </customfield_read>
    </resources>
</global>

thanks