Hi, I have created one single certificate that contains the two domains “domainA.com” and “domainB.com”. Both webs do use the same web-server, but only different directories. For domainA.com the SSL works perfect. Now accessing the domainB.com the error DLG_FLAGS_SEC_CERT_CN_INVALID is shown. The message from SSL-Checker says: "None of the common names in the certificate match the name that was entered (domainB.com). You may receive an error when accessing this site in a web browser.
Without real domains to look at, I would have to guess that you only typed in the first domain when you used https://www.sslforfree.com/
You need to list both domains, separated by spaces, to have them both listed on your certificate. Just go back to https://www.sslforfree.com/ and request a new certificate listing both domains, and replace your old certificate with this new one, and you should be all set.
The other possibility is that you have two (or more) virtual hosts in your web server, and you did something to tell the web server to associate the certificate with one of the virtual hosts, but not with the other. In that case the web server would only know to present the certificate in response to requests related to one domain, but not to the other.