Help Me with an Invalid Feed

I just made a new post on my wordpress blog (http://www.rjmartino.com) but found out that my feed is not valid by using Feedvalidator.com.

http://feedvalidator.org/check.cgi?url=http%3A%2F%2Fwww.rjmartino.com%2F

Can someone tell me how to fix this? Or, how to begin troubleshooting this problem.