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:
$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?