Some RSS Feeds Not Working

[rvb123]

So When testing the RSS reader on the player, some of them don't show up. I figured It was the fact that the player deletes files that are old (in my case 2 weeks). So I went and actively looked for something that was 'younger' than 2 weeks but still nothing.
The site I was attempting to test was http://www.fanfiction.net/
Is it a problem with that specific website or is there an underlying problem with the player? I also tested it on Reddit and it worked fine.