It looks like you're generating the SSL certificate as a self-signed entity, is this correct? Is that Internet Explorer in your screenshot? It's possible that IE is detecting that the certificate is not signed by a valid signing authority, or that the address you are using to reach the Tableau Server is not what is listed in the certificate. It's hard to say without seeing the certificate details or exact error message underneath that warning.
That being said, you might want to take a look at this article: Obtaining an SSL Certificate for Tableau Server | Tableau Software
Hope this helps!