This function in emfield.rss.inc seems to be causing rss to be malformed.

Yes, my RSS feeds were broken until I found http://www.drupal.ru/node/19118 (sorry if you do not know Russian :))

But the following change works and resolves the 0="xmlns:media=http://search.yahoo.com/mrss/ problem:

change in emfield.rss.inc, line 123

// Workaround for http://drupal.org/node/157709.
static $been_here = FALSE;
if (! $been_here) {
/* change start - fix the next line as per http://www.drupal.ru/node/19118
$rss[] = array('namespace' => array('xmlns:media="http://search.yahoo.com/mrss/"'));
*/
$rss[] = array('namespace' => array('xmlns:media' => 'http://search.yahoo.com/mrss/'));
// change end
$been_here = TRUE;
}

This is a duplicate of #301741: RSS Feed: XML Media Namespace Not correctly set. A patch was provided in that issue (implementing the same fix as proposed in #1).

Thanks- this is already applied to the dev version...