Ignore it. When accessing cPanel through a secure (https) connection with SSL, you will always get a complaint that the certificate name (vader.lunarmania.com) doesn't match the actual server name (login.vader.lunarmania.com). It's harmless (in this case). You may be able to tell your browser (IE?) to shut up about it. An alternative is to access cPanel through a non-secure (http) connection:
http://www.yourdomain.com/cpanel. You won't get the warning and response will be much faster, but be aware that you shouldn't transmit sensitive information such as passwords or credit card numbers in either direction, as they are not encrypted.