Hi again Gordon,
So sorry to be bombarding you at the moment. I've been hoping to put this off but I can't do so any longer!
I tried adding a Xerte exercise to Taskchain. I uploaded the whole folder which contains all the files needed to run the Xerte, including the index.html. On my Moodle, Taskchain displays a white square where the screen of the exercise should be. I tried on your test site with the same result.
Do I need to do something further to instruct Taskchain to link to the index.html file?