The Internet Explorer needs to cache the requested data in order to hand it over to the ActiveX object. If no-cache is enabled in the headers being sent, the request is not passed to FSI Viewer.
Instead of using the no-cache directive, please use a new header. If you are using eRez, you will have to add this to the “WEB-INF/private/headers.xml”. Considered you named the header definition “https” you can activate this via the effects parameter, e.g. “&effects=header%3Dhttps”