RSS Content:encoded tag error

I’m getting extra code showing up in my RSS feed after the end of the content. Customer support at MailChimp helped me identify the problem: the <Content:encoded> tag is not properly closing at the end of my post content. Here is a screenshot of the error: http://screencast.com/t/Yc7rp3gCrK6

Here is what that is outputting: http://us12.campaign-archive1.com/?u=192159187ec26dc9ef166a297&id=bd450d116f

Question is: how do I fix it?

Thanks for any help you can provide!