This error message is displayed on computers running Windows Vista if the option “check for server certificate revocation” is enabled in IE 7 and if the SSL certificate does not contain a CRL value (certificate revocation list). Vista may trigger this warning when an SSL connection is made to the server.
If this is the case, Vista clients will not be able to register with the administration server until they have performed the following:
> Go to Internet Explorer > Tools > Internet Options > Advanced tab > Security options and uncheck “Check for server certificate revocation (requires restart)”.
As an alternative you can connect to the administration server using the IP address rather than the domain name OR connect using an HTTP connection instead of HTTPS.