Fix me! This should issue an error on using existing email addresses in shopplugin. It should be places in functions.php. It just doesn't work now.. I get 500 (Internal Server Error).

gistfile1.txt

add_filter('shopp_customer_registration','ihc_registration_data_validation');
function ihc_registration_data_validation() {

    if (shopp_email_exists($_POST['email'])) {
        new ShoppError(__('Email address is already registered with another Shopp customer.','Shopp'), SHOPP_ERR);
    }

    return $_POST;
}