Unfortunately if you're seeing this message you either have 1 of 2 problems. Either you're visiting a site with an incorrect SSL Cert or your visiting a site with an expired SSL Cert.
If it's an expired SSL Cert, then the obvious fix is to renew the cert and install it. If the Cert is still valid but not cofigured correctly, IE7 now will do you a favor and block the content.
The main issues with incorrectly configured SSL certificates seems to be the "Issued to" field. It should be read the URL of the site, rather than the contact information. IE6 didn't care about this field but IE7 takes it very seriously.