RSS Feed Broke

For some reason, my global feed no longer works. When I try to implement the feed I get the following error message.

RSS Error: XML error: EntityRef: expecting ';' at line 224, column 72

Any idea what is causing this?

The plugin is installed here. The current RSS feed is provided by Feedburner. It is not generating any feeds. The error message shows up on this site, which uses the RSS feed from the original site. The error message appears in the right side bar near the top.