"Attributes construct error" in RSS Feed?

Trying to help fix a site that has issues with it’s RSS feed. It loads part of the feed, then stops and gives a big pink error at the top of the page:

This page contains the following errors:
error on line 101 at column 36: attributes construct error
Below is a rendering of the page up to the first error.

Any ideas? I’ve switched the site to Twenty-Eleven, and disabled all plugins, but it still occurs. No change. The core files should not have been modified in any way…. I’m just out of ideas. Any help/ideas appreciated.

Here is the feed: http://thisweekinmormons.com/feed/