iTunes can't verify the identity of the server mp3s.nashownotes.com

I have tried to continue listening to the No Agenda podcast after a pause for a few months and today I get the error message:

iTunes can't verify the identity of the server mp3s.nashownotes.com

I have tried to unsubscribe and delete the podcast and then subscribe to it again, but I get the same error message again. When I go to the server (web page) with a web browser, I see no certificate or security problems.

Any recommendations what I should do to be able to listen to the podcast using iTunes instead of going to the No Agenda website?