I have recently purchased an SSL certificate for a client from http://www.positivessl.com/. The $49per year certificate. It has been installed and works on most browsers.
However, our client has a large number of Windows XP SP3 machines that are running Internet Explorer 8. The environment cannot easily be updated. When they hit the website, Internet Explorer shows a page not found error. They certificate supports TLS1.0 and they have it enabled in IE8 setting. They do not have either TLS1.1 or TLS1.2 available too them.
I have also just installed 4 Comodo Posstive SSL certificates for my 4 e-commerce shops. I know that this certificates is not supported by Windows XP using IE8, and will never be. But I have seen many other sites using SSL that works fine on Windows XP.
PositiveSSL works just fine with IE 8 on Windows XP. Since you have a good number of sites, you may want to open a support ticket via https://support.comodo.com so that we may assist you directly.
I bought my certificate through Dreamhost, but it is a comodo certificate. Any help would be appreciated. Dreamhost referred me to MS, but support for XP is ending soon they aren’t going to be any help to me.