paypal sand box and confirm order

I have configure a try server with xampp and a sanbox with us paypal pro.
In global page I set sandbox true and correct username psw and api.
I try to buy a product but when check out with paypal button I go to pp_checkout_failure.php page. What is the problem?

There could be a couple of things going on. You are probably experiencing a problem with either the shipping or the checkout. If you can see a shipping variable in the URL when you get the checkout failure page then it is a shipping problem. If you don't see this then it is probably a checkout issue. You will need to add in the request and response info for the part that is not working to see what the problem is.

If you see shipping=fail in the URL when you get to this page post back and let us know the shipping provider you are working with.

If you do not see this in the URL follow these steps to get the debug info to show:
showpost.php?p=34342&postcount=3

I have insert the code
<?php echo $WA_PP_ECO_DoResult->fullRequest; ?>
<br/><br/>
<?php echo $WA_PP_ECO_DoResult->fullResponse; ?> in pp_checkout_failure.php page and the error is:
Warning: session_start() [function.session-start]: Cannot send session cache limiter - headers already sent (output started at C:\xampp\htdocs\mysite.it\pp_checkout_failure.php:3) in C:\xampp\htdocs\mysite\WA_eCart\WA_eCart_Definition_PHP.php on line 479

I attach files

This code must go in the page where you would like to see the error. I have added the code to the page for you in the rite spot, please give it a try with this updated page.

I try updated file pp_checkout_failure.php but no have error, only normal message: Your PayPal transaction could not be completed. Please return to checkout and try again.
Also I have set WA_Globals.php with:

//PayPal Settings
$WAGLOBAL_Paypal_Sandbox = "true"; //Set to true if you wish to use the PayPal Sandbox for testing transactions.
$WAGLOBAL_Paypal_User = "myusername";
$WAGLOBAL_Paypal_Password = "mypassword";
$WAGLOBAL_Paypal_Signature = "mysignature";

where is the problem?

Do you have a link where this can be seen at? It seems that you are doing things correctly if you have entered your account details into the globals file and are testing it properly. What is the result you get if you attempt to run a credit card transaction?

When you get the error message about the transaction not being completed what page are you on when you see this? Have you checked on the test mode setting in the globals:

$WAGLOBAL_Test_Mode = false;

You must have the test mode set to false in order to test transactions.