Sadly I don't have an answer, but I'm having a similar problem. We actually have a feed through Feedburner. My web site mate has a podcast and tried to get it submitted into iTunes, and since then our feed has not worked (so the aggregators like elbo.ws and Facebook aren't pulling our site, so our traffic went from 2,000 views per post to 20. literally). It says the feed is not validated. I found a site that says "Validate your feed" (www.feedvalidator.org - you might wanna check it out babadoux) but when I enter in my url, it says my feed WILL NOT validate.
It even gives me the line item list of why, for example, "Undefined itunes_summary element: object" - but I don't understand where I would go in to edit this. I might check within WordPress, but I think since it's a plugin I can't alter it myself. Or if I could just undo us applying to get our podcast on iTunes...any advice would be grand!