Error: Security header is not valid. This is the response I get when I try click the "Test" button within the extension set-up.
Error Log:
2013-10-17 8:22:40 - App Warning: AbanteCart core v.1.1.7 PayPal Express Checkout Error: Security header is not valid. Test mode = 1. in /home/user1/public_html/extensions/paypal_express_checkout/admin/controller/responses/extension/paypal_express_checkout.php on line 82
2013-10-17 8:23:31 - App Warning: AbanteCart core v.1.1.7 PayPal Express Checkout Error: Security header is not valid. Test mode = 1. in /home/user1/public_html/extensions/paypal_express_checkout/admin/controller/responses/extension/paypal_express_checkout.php on line 82
2013-10-17 8:27:45 - App Warning: AbanteCart core v.1.1.7 PayPal Express Checkout Error: Security header is not valid. Test mode = 1. in /home/user1/public_html/extensions/paypal_express_checkout/admin/controller/responses/extension/paypal_express_checkout.php on line 82
Please help! no clue on what to do.