Q: iTunes Producer is stuck at Authenticating with the iTunes Store.

I'm trying to update my ebook and it keeps getting stuck at the Authenticating with iTunes Store stage. I've done this before and have had no problems. Usually it takes a few seconds to a minute at the most. This time, I let it sit for close to 15 minutes. I don't think it's Authenticating. I've cancelled and tried again and again but nothing. What gives?