Cannot sign in to iTunes

I am on a 2015 MacBook Air running OS X El Capitan and iTunes 12.3.04. I also have Apple Music service.

Initially, I was troubleshooting why an album that I had added to My Music before its release didn't automatically appear as complete in My Music once the album released. In the process, I logged out of iTunes and attempted tog back in to see if this would fix my issue. However, I couldn't log back in and got this error message:

Main question: Why can't I log back in?

Secondary question: Why does an album not show complete after its release?