I know this is not an RSS issue, but this will solve not found errors. Give it a try.
Create a custom 404 error page with following code
<?php
$_SERVER['REQUEST_URI'] = substr($_SERVER['QUERY_STRING'], strpos($_SERVER['QUERY_STRING'], ':80')+3);
$_SERVER['PATH_INFO'] = $_SERVER['REQUEST_URI'];
include('index.php');
?>
Then add this page to the domain settings under error category for 404 error and refresh & save the permalink structure. That's it ...you will have fun..