That old error from Zen Cart came back again.
I have recently moved the site and had to make the 2 changes in code for PayPal to send the correct country code to the shopping cart in order to calculate the shipping.
For those running 1.38a and do a fresh install here is a reminder of the changes:
/includes/modules/payment/paypal/paypal_curl.php
and the zen cart fix for:
line 1825 in /includes/modules/payment/paypalwpp.php from
It was only over the course of a few hours since going live that this error was spotted and all is working well now. Once again apologies to anyone inconvenienced by this.