invalid rss feed

Here is the first bit of wp-rss2.php:

<?php
if (!isset($feed) || !$feed) {
$blog = 1;
$doing_rss = 1;
require('wp-blog-header.php');
}
header('Content-type: text/xml; charset=' . get_settings('blog_charset'), true);
$more = 1;
?>
<?php echo '<?xml version="1.0" encoding="'.get_settings('blog_charset').'"?'.'>'; ?>

I tried squishing everything up into 1 php block with no blank lines, but that didn’t make any difference. I also tried commenting out the header call, but that just made things worse.

phew, that was a journey…
I went from wp-rss2.php to wp-blog-header.php to wp-settings.php and finally tracked it down to the moment when the plugins get loaded. Then I went through each plugin until I tracked it down to random_file.php, which turned out to have a couple of stray ctrl-m characters at the end. Cleaned that up, et voila, a valid rss feed!

in my case a beta of Textile 2 was messing up the feed