[wp-hackers] Some feeds will not display

[RePost]

I've been unable to get WordPress to display any feeds other than RSS, 
FeedBurner and comments.

RSS2, Atom, main feed (mysite.com/feed) and categories feeds show a 
blank screen in Firefox and a "The page can not be displayed" message in IE.

I've disabled my FeedBurner redirect plugin, but can't think of any 
other settings that may be affecting my feeds.

Here's what I've got in header.php:

    <link rel="alternate" type="application/rss+xml" title="RSS" 
href="http://feeds.feedburner.com/MyFeed" />
    <link rel="alternate" type="application/rss+xml" title="RSS 2.0" 
href="<?php bloginfo('rss2_url'); ?>" />
    <link rel="alternate" type="text/xml" title="RSS .92" href="<?php 
bloginfo('rss_url'); ?>" />
    <link rel="alternate" type="application/atom+xml" title="Atom 0.3" 
href="<?php bloginfo('atom_url'); ?>" />
    <link rel="alternate" type="application/rss+xml" title="RSS" 
href="<?php bloginfo('comments_rss2_url'); ?>" />
    <link rel="pingback" href="<?php bloginfo('pingback_url'); ?>" />

Any suggestions?

Thanks.