We have just installed an SSL certificate on the following domain:

https://www.floorheatingonline.com/

In all browsers apart from IE there are no security warnings and there are no references to insecure pages in the HTML.

In IE on some computers we are seeing the following warning:

There is a problem with this website's security certificate

The security certificate presented by this website was not issued by a trusted certificate authority.
The security certificate presented by this website was issued for a different website's address.

Security certificate problems may indicate an attempt to fool you or intercept any data you send to the server.

We recommend that you close this webpage and do not continue to this website.
This is only happening on some computers though, we have one computer in the studio this is happening on and another that it is not. (We have checked the computer's clock).

Has anyone come across an issue like this in the past?