I found myself locked out of my own site with a notice that "'Your account has to be confirmed by an administrator before you can login."
Unfortunately I didn't immediately suspect this plugin, but deactivated Buddypress, BBpress (latest versions) and several other plugins before noticing this one.
In the first instance, the login would not accept my password. So I requested a password reset. Then I got the error message above.
I had to FTP into the account to remove the plugin.
I want to be able to approve new users, but this was scary!!