If all else fails, try resetting the password manually in the database. This envolves selecting a new password, "MD5'ing" it using, for instance the PHP md5() function, and inserting the MD5 hash into the password_hash field of the ezuser database in the row corresponding with your user account (usually contentobject_id 14 if you're the main admin).
Could be a solution if your password has changed.
I experienced such kind of problems with an unproper session expiration.
Try to delete all old session or reboot to get a new IP (if it's apply to you). Cheers..
