It seems as though there is a feed error with WordPress 1.5.1. To fix this go to wp-blogheader.php at line 36 and replace
((strtotime($client_last_modified) >= strtotime($wp_last_modified)) && ($client_etag == $wp_etag)) :
((strtotime($client_last_modified) >= strtotime($wp_last_modified)) || ($client_etag == $wp_etag)) ) {
if ( preg_match(‘/cgi/’,php_sapi_name()) ) {
header(‘Status: 304 Not Modified’);
echo “\r\n\r\n”; ?>
with
((strtotime($client_last_modified) >= strtotime($wp_last_modified)) && ($client_etag == $wp_etag)) :
(($client_last_modified && strtotime($client_last_modified) >= strtotime($wp_last_modified)) || ($client_etag == $wp_etag)) ) {
if ( preg_match(‘/cgi/’,php_sapi_name()) ) {
header(‘Status: 304 Not Modified’);
echo “\r\n\r\n”; ?>