1) No way to tell at this point how simple or complex the problem is.
2) Not necessarily, but we can add code to the confirm page to help us troubleshoot.
on the confirm page, add the following code just before the closing </html> tag:
<?php
@session_start();
echo "<p>FedEX: <br />";
echo "Full Request: ".(isset($_SESSION["WA_Store_Cart_FedEx_FullRequest"])?htmlentities($_SESSION["WA_Store_Cart_FedEx_FullRequest"]):"n/a")."<br />";
echo "Full Response: ".(isset($_SESSION["WA_Store_Cart_FedEx_FullResponse"])?htmlentities($_SESSION["WA_Store_Cart_FedEx_FullResponse"]):"n/a")."<br /></p>";
?>
this will show the request being sent to fedex and the response coming back from them to help us see what may be wrong.