I am having this issue too. I think the site users who are being blocked out have mistakenly tried to use an invalid username or tried too many time with the wrong password (other users are getting in just fine).
BUT, I'm not seeing these users or their IP addresses as having been blocked, and there doesn't seem to be a way to remove the block for these clumsy but valid users--other than to let it expire.
Anyone have any ideas about what is going on?
