just incase anyone else is experiencing this error (l was), l followed the instructions given, and got the following fatal error:

Fatal error: Call to undefined method ot_insurance::get_order_total() in /home/xxxx/public_html/products/includes/classes/order_total.php on line 181

l then looked for and found an old shipping insurance module in admin that l was no longer using, turned it off, and voila, everything worked again.