SSL certificates are issued to a fully qualified domain name, or IP address, known as the common name. When accessing a page via https the URL must match the common name that the certificate is issued to. For example: if a certificate is issued to
http://www.example.com/, and a user attempts to access the page using https://example.com/, they will receive this error. The same rule applies to linking secure sites. The only exceptions to this are multidomain certificates and wildcard certificates, which support different domains and subdomains respectively.