I had the same problem when I tried to hook into a hotel internet connection.
Assuming you are using GNOME, you need to:
1. Go to Preferences, then Administration, then click on 'Users and groups.'
2. Go to root user properties.
3. Set the password to something very secure.
4. Apply and close window. Now go to Preferences > Administration > Login Window > Security
5. Enable root login at login window.
6. Log out.
7. Log in as username root and your new root password.
That's all it took for me.
Good luck! Post back here if it does not work.