none of my podcast are updating

Since July 7th none of my podcast have updated. I can see that new episodes are available for each that I subscribe to but they just won't update. For example I listen to "The Nerdist" and I can see 2 new episodes are available in the iTunes store but they won't update in my iTunes. Even when I click to download them from within the iTunes Podcast store all that shows up is a faded selection with an exclamation mark, but thats it. Any ideas about what the issue is?