This is a bug in phpMyAdmin. My MySQL database user has no password, and is thus locked. I entered no password with allow no password enabled, and I get this error:
Login without a password is forbidden by configuration (see AllowNoPassword)
It is a bug. What's wrong?
Login without a password is forbidden by configuration
UPDATE: I upgrade my phpMyAdmin version to 3.5.2. Same error.
Look for AllowNoPassword in Documentation.html for an explanation, and change the setting in config.inc.php to allow it.