I don't support the Brightmail product, but with SEP, this usually indicates that the machine can't connect to our website. Please make sure that the account that is used to run the page where you should see the site is able to access this website:
http://securityresponse.symantec.com
The account may be the system account as well. So I suggest making sure that this site can be passed through your firewall/proxy.
Again I do not support this product, so I may be completely wrong with this suggestion. If this does not work I apologize for wasting your time.