[Hans]

I have seen that you fixed it already.
When i visit your site i have no errors with any browser.

Nevertheless, i like to give this info as well:

If you want to use a SSL certificate for a web on your server:

Whithin ISPConfig, on the basic tab of the website which needs SSL, you enable SSL.
Then click on the options of that site and then on the SSL tab.
There, you can put your certifate for your website.
(One certificate / IP).