The string was not recognized as a valid DateTime

Hi, I downloaded a rss feed reader. It works fine if I'm reading from this url http://weblogs.asp.net/scottgu/rss.aspx which is the author who wrote the rss feed reader,  but if I change to http://rss.cnn.com/rss/cnn_topstories.rss it gives me the following error

"The string was not recognized as a valid DateTime. There is a unknown word starting at index 26."

Line 29:         var posts = from item in rssFeed.Descendants("item")
Line 30:                     select new
Line 31:                     {
Lin ...