This error is telling you that the certificate used by your site is actually issued for another site. This is not safe operation.
shared SSL should be OK if you configure this properly in your hosting. This what I found
http://support.hostgator.com/articles/hosting-tools/ssl-certificates/how-to-set-up-and-use-your-shared-sslAlso very common error is when sub domain is accessed that is different from certificate domain. For example, you may have entered site with
https://domain.com, but the certificate is for
https://www.domain.com. In this case, if you access
https://www.domain.com directly, you should not receive the warning