Fatal error

I am placing test orders on the website I am managing. I placed 2 orders successfully, but am now getting the error message on the checkout page after I enter a test credit card number:
Fatal error: Call to undefined method WC_Order_Item_Meta::new_order_item() in /home/content/26/7477426/html/wp-content/plugins/woocommerce/classes/class-wc-checkout.php on line 414

The line of code in question is:
$item_meta->new_order_item( $values );

The site is