UPS vs USPS if international

I'm added UPS & USPS profiles using the eCart add shipping - then I added a function

<?php
if(isset($_SESSION["eCartCheckoutForm_shipping_country"]) && $_SESSION["eCartCheckoutForm_shipping_country"] != "") {
$_SESSION['shipUS'] = substr($_SESSION["eCartCheckoutForm_shipping_country"],0,2);
}
?>

and applied a trigger if shipUS = US to UPS and a if shipUS != US to USPS in eCart shipping rules

It seems to work for UPS but I'm getting this error for USPS and when I click the checkout button


Warning: Cannot modify header information - headers already sent by (output started at /home/grandold/public_html/confirm.php:34) in /home/grandold/public_html/confirm.php on line 418

: Cannot modify header information - headers already sent by (output started at /home/grandold/public_html/confirm.php:34) in /home/grandold/public_html/confirm.php on line 596

Thanks!

this error happens when there is output between php tags, see this post for details
showthread.php?t=19285


according to the error, the output is at line 34:
output started at /home/grandold/public_html/confirm.php:34