Please email me cio [at] rawvoice dot com the contact at Apple who told you which feed to use. That in itself is a problem, they should be aware that the podcast feed is the feed you should be using. The rss2 feed, while it may work, also includes blog posts which is not what you should use for iTunes (according to Apple's podcast specifications).
The podcast feed (
http://stateofshakespeare.com/?feed=podcast) is prematurely ending, an indication that either something is crashing on your server (a theme or more than likely a plugin) or your server is running out of memory. Switching to the blog feed may fix this now but more than likely this problem will come back. You really need to figure out what is causing the issue first.
More than likely this problem started after you updated a theme or plugin, which may give you a hint as to what theme or plugin is causing the problem.
To diagnose, use these steps:
http://create.blubrry.com/resources/powerpress/using-powerpress/diagnosing-feed-andor-player-issues-with-powerpress/When the feed is working, it will end with </xml>. Currently at the bottom of your feed you can see it is starting a new <description> section and then ends prematurely.
Please let me know what theme or plugin is causing your issue.
If you are down to only your theme and just PowerPress plugin and you still have the feed prematurely ending, then it may be a server memory issue. The only way to solve that is to change the "items per feed" setting in PowerPress > Feeds section. The WordPress recommended value for this is 10.