When I go to the site and try to test the Express Checkout it seems to be going directly to the failure page and not getting to PayPal at all. This tells me that the authenticate API call is not occurring successfully. If you have just changed it out of the sandbox mode then the most likely problem is that you are referencing the wrong API credentials or the ones you are using are not properly configured to allow the Express Checkout.
To get some more details about what is occurring add this code to your checkout failure page and test this out:
php:
<?php
if(!session_id()) session_start();
echo("Direct Pay Full Request :<br />");
echo("<code>".isset($_SESSION["PP_DirectPayment_postedValues"])?$_SESSION["PP_DirectPayment_postedValues"]:""."</code><br /><br />");
echo("Direct Pay Full Response :<br />");
echo("<code>".isset($_SESSION["PP_DirectPayment"])?$_SESSION["PP_DirectPayment"]:""."</code><br /><br />");
echo("PayPal Express Checkout requests and responses :<br />");
echo("Auth request: ".isset($_SESSION['ECO_Auth_Request'])?$_SESSION['ECO_Auth_Request']:""."<br /><br />");
echo("Auth Result: ".isset($_SESSION['"ECO_Auth_Result'])?$_SESSION['ECO_Auth_Result']:""."<br /><br />");
echo("Get Request: ".isset($_SESSION['ECO_Get_Request'])?$_SESSION['ECO_Get_Request']:""."<br /><br />");
echo("Get Result: ".isset($_SESSION['ECO_Get_Result'])?$_SESSION['"ECO_Get_Result']:""."<br /><br />");
echo("Preocess request: ".isset($_SESSION['"ECO_Process_Request'])?$_SESSION['ECO_Process_Request']:""."<br /><br />");
echo("Process Result: ".isset($_SESSION['ECO_Process_Result'])?$_SESSION['ECO_Process_Result']:""."<br /><br />");
?>
Post back with what you get after testing this out.
