I had the same issue, but figure it out after a few days...
The problem was that I had formerly always used the username and password boxes under the "Did you miss your activation email?" well after being a registered user.
That no longer works for login of already-registered users, and seems to be reserved for new members needing to enter their initial registration activation.
So now I just use a login-link which takes me to a small window which works as an already established user.
Took me a few days of head scratching.