Yes, i see the problem, there is a broken tag at the very begining of the rss content. Looking at the page the break is caused by one of your plugins giving a 404 error - Tweetmeme
Failed to load resource: the server responded with a status of 404
(TweetMeme button shutdown) http://tweetmeme.com/i/scripts/button.js
Would you please update or disable the plugin and see if the problem goes away. Also it looks like your w3 total cache plugin is not functioning correctly since its not minimizing the content while comment on bottom of source says it is. Perhaps once that twitter plugin starts working everything will fall back into place.