I had the same issue and a new post did not work.
My issue was that the WordPress URL was different from the Site URL. Once I updated the feed url (e.g. http://sitename/wordpress/?feed=podcast) to match the site URL (e.g. http://sitename.org/?feed=podcast) itunes accepted the feed fine.
Thanks for a great plug in!
AdventureChick
Can you share how you fixed your issue?