Joomla 3.3 unable to login as administrator

Question

I've actually answered this question, but thought I'd put it up here to save anyone else the wasted hours since upgrading to 3.3.

I was able to login at the front-end, so knew the password was working. However, it just returned to the login screen without error in /administrator.

Answer 1

Edit the configuration.php file in the root directory and make sure that the cookie domain is either has www. prefixed or not depending on your host's preference.