If you're using IE11 and install InstantForum or InstantKB on a secure HTTPS site you may encounter a problem loading InstantForum or InstantKB if you link to your installations from a non-secure site.

This is not a problem within our software but a known issue within IE11 on 8 & 8.1 after installing Cumulative Security Update for Internet Explorer 11 (KB2925418) for Windows 8.1 for x64-based systems 

Solution 

The quickest way to resolve this problem is to edit go to Options within Internet Explorer > Advanced. Scroll down to the very bottom and un-tick "Watn if changing between secure and not secure mode". 

Unfortunately there is no know server side fix for this and it will require adjusting settings on the client.