The Root Certificates and/or Intermediate Certificate(s) may not be installed correctly. This can be checked by clicking on 'View Certificates' when you get the error message and seeing if all three certificates are visible.
It may also be that the certificate being used is not for the Fully Qualified Domain Name, check again using 'View Certificates' to see if the domain name on the certificate matches the domain name in the URL that you are going to.
Check your Internet Option' and make sure that 'Use SSL 3.0' is ticked in the 'Advanced' section.
Why does the secure part of the website say the name on the security certificate is invalid or does not match the name of the site?