I've tried it across three sites using two different hosting services, and I've gotten the 500 error every time. One site was using a fresh install of Wordpress.
If I enter the wrong username, I am presented with "Unable to retrieve account information."
If I enter the wrong password, I am presented with "Authentication failed. Please make sure the password is correct then try again."
If I enter everything correctly, I am presented with "HTTP 500 Internal Server Error"
Would both these servers be blocking api.blubrry.com by default? If so how do I allow it?