The document download requires a logging into the restricted part of the website. Do you think that might be the issue?

Just updated the download code to

<a href="http://itso.int/images/stories/IAC-20/IAC-20-Convening-Letter-EN.pdf" onclick="document.getElementById('trackdownload'.src='http://itso.int/index.php?option=com_jrealtimeanalytics&track=2&lang=en'">Refree.:10-29-15/DG-59</a> <iframe id="trackdownload" style="display:none" src=""></iframe>


Custome URL to
http://itso.int/index.php?option=com_jrealtimeanalytics&track=2&lang=en


Let's see.