XML : Issue Parsing RSS XML in Swift

I built an XML RSS reader app using a tutorial and up until now, I haven't had any trouble parsing RSS feeds. But I combined a bunch of feeds into one xml feed using this site RSSMix.com and now it's throwing up an exception.

  "Index 3 out of bounds; string length 1".     

I'm still pretty new to iOS development and I'm a little confused about which index this would be referring to. As far as I know, the xml structure is the same as the other ones I was successful with. Any help would be very much appreciated!

Thanks.