Hello again Rossana,
after a little more investigation and thought, I decided to modify the HotPot and TaskChain modules so that they will detect and remove any of the ascii control chars that are not allowed in XML files, such as the ascii-31 char that was present in your jqz file.
Also, I noticed the the images in your JQuiz, which use "float: right" CSS to position the images on the right of the question area, overflow the question box, so I added some CSS which should prevent the images overflowing in this way.
As a result, you don't need to change any of your HP exercise files, you simply need to arrange for the HotPot module on your Moodle site to be updated at the next convenient opportunity, and the new functionality will be available to you.
Thanks you for alerting me to this issue, and for providing a file to test on.