Same problem as a couple of others I've seen here:
The requested URL /login/ was not found on this server.
Additionally, a 404 Not Found error was encountered while trying to use an ErrorDocument to handle the request.
That's the message I get when I try to login or logout through the plugin.
I'm running 3.5 on a new OS X Mountain Lion Web Server. The permalinks are still on default and I haven't touched the .htaccess file
With the plugin activated, I can login through the backdoor ( http://yourDomainName.com/wp-login.php?no-redirect=true) without any problem.
Any ideas? I've tried everything that was obvious to me to no avail.