Could you check if Xibo is using IE11? ( Enabling HTML5 in the Windows .net Player )
1.7.8 client does this registry change during installation, so it should be ok.
I assume layout id 6 is the layout you want to display on this client? So it seems that it did download everything it needs.
I assume your webpage is publicly accessible over the internet and all of your clients have internet access?
If we can reach this page, you can export your layout and send to me and I’ll have a look. (upload to dropbox/similar and share the download link with me here or via pm).