Okay - this is so very odd.
Since I was having problems, I read this post over 3 days ago, and changed my password. When I used this password for the past 3 days when attempting to setup my mail client, I still recieved the "invalid username or password" error.
Just for giggles, I changed my password again 10 minutes ago, and tried this "new" password on my mail client. Still didn't work....
So, for even more giggles, I tried my older password (the one I created 3 days ago). Guess what... it works!
Oh my, Apple, what do you have going on there in your world????
P.S. - For my Android phone, I needed to use TLS for security for Outgoing Mail, not SSL. SSL on Incoming Mail works just fine.