when you make changes to the gateway settings, you need to upload the webassist/ecart/checkout/credentials/gateways.php file to the server.
if you close the browser completely to start a new browsing session before testing the checkout, you wont see the other forms details in the session dump.
the end of the session dump:
["PP_DirectPayment"]=> string(2055) "2014-04-08T16:29:08ZFailureb868613592300Security errorSecurity header is not valid10002Error60.010433064" }
shows the response from paypal.