WooCommerce Добавить в корзину ошибка кнопки

В WooCommerce variable.php у меня есть этот код:

<?php
/**
* Variable product add to cart
*
* @author      WooThemes
* @package     WooCommerce/Templates
* @version     2.1.0
*/

if ( ! defined( 'ABSPATH' ) ) exit; // Exit if accessed directly

global $product, $post;
?>

<?php do_action( 'woocommerce_before_add_to_cart_form' ); ?>

<form class="variations_form cart" method="post" enctype='multipart/form-data' data-product_id="<?php echo $post->ID; ?>" data-product_variations="<?php echo esc_attr( json_encode( $available_variations ) ) ?>">
<?php if ( ! empty( $available_variations ) ) : ?>
<table class="variations" cellspacing="0">
<tbody>
<?php $loop = 0; foreach ( $attributes as $name => $options ) : $loop++; ?>
<tr>
<td class="label"><label for="<?php echo sanitize_title($name); ?>"><?php echo wc_attribute_label( $name ); ?></label></td>
<td class="value"><select id="<?php echo esc_attr( sanitize_title( $name ) ); ?>" name="attribute_<?php echo sanitize_title( $name ); ?>">
<option value=""><?php echo __( 'Choose an option', 'woocommerce' ) ?>&hellip;</option>
<?php
if ( is_array( $options ) ) {

if ( isset( $_REQUEST[ 'attribute_' . sanitize_title( $name ) ] ) ) {
$selected_value = $_REQUEST[ 'attribute_' . sanitize_title( $name ) ];
} elseif ( isset( $selected_attributes[ sanitize_title( $name ) ] ) ) {
$selected_value = $selected_attributes[ sanitize_title( $name ) ];
} else {
$selected_value = '';
}

// Get terms if this is a taxonomy - ordered
if ( taxonomy_exists( sanitize_title( $name ) ) ) {

$orderby = wc_attribute_orderby( sanitize_title( $name ) );

switch ( $orderby ) {
case 'name' :
$args = array( 'orderby' => 'name', 'hide_empty' => false, 'menu_order' => false );
break;
case 'id' :
$args = array( 'orderby' => 'id', 'order' => 'ASC', 'menu_order' => false, 'hide_empty' => false );
break;
case 'menu_order' :
$args = array( 'menu_order' => 'ASC', 'hide_empty' => false );
break;
}

$terms = get_terms( sanitize_title( $name ), $args );

foreach ( $terms as $term ) {
if ( ! in_array( $term->slug, $options ) )
continue;

echo '<option value="' . esc_attr( $term->slug ) . '" ' . selected( sanitize_title( $selected_value ), sanitize_title( $term->slug ), false ) . '>' . apply_filters( 'woocommerce_variation_option_name', $term->name ) . '</option>';
}
} else {

foreach ( $options as $option ) {
echo '<option value="' . esc_attr( sanitize_title( $option ) ) . '" ' . selected( sanitize_title( $selected_value ), sanitize_title( $option ), false ) . '>' . esc_html( apply_filters( 'woocommerce_variation_option_name', $option ) ) . '</option>';
}

}
}
?>
</select> <?php
if ( sizeof( $attributes ) == $loop )
echo '<a class="reset_variations" href="#reset">' . __( 'Clear selection', 'woocommerce' ) . '</a>';
?></td>
</tr>
<?php endforeach;?>
</tbody>
</table>

<?php do_action( 'woocommerce_before_add_to_cart_button' ); ?>

<div class="single_variation_wrap" style="">
<?php do_action( 'woocommerce_before_single_variation' ); ?>

<div class="single_variation"></div>

<div class="variations_button">
<?php woocommerce_quantity_input(); ?>
<button type="submit" class="single_add_to_cart_button button alt"><?php echo $product->single_add_to_cart_text(); ?></button>
</div>

<input name="add-to-cart" value="<?php echo $product->id; ?>" />
<input type="hidden" name="product_id" value="<?php echo esc_attr( $post->ID ); ?>" />
<input type="hidden" name="variation_id" value="" />

<?php do_action( 'woocommerce_after_single_variation' ); ?>
</div>

<?php do_action( 'woocommerce_after_add_to_cart_button' ); ?>

<?php else : ?>

<p class="stock out-of-stock"><?php _e( 'This product is currently out of stock and unavailable.', 'woocommerce' ); ?></p>

<?php endif; ?>

</form>

<?php do_action( 'woocommerce_after_add_to_cart_form' ); ?>

Но когда я выбираю размер и затем нажимаю «Добавить в корзину», я получаю сообщение об ошибке «выберите параметры продукта».
Кто-нибудь знает, как это исправить? Это как форма и кнопка не работают «вместе».
Заранее спасибо.