clicknupload.org uses HTTPS only. Can you report the problem from program via right click? If you open the site from browser with HTTP, it is not redirected to HTTPS but it fails?
In many countries the http version of clicknupload is blocked while https version of it works perfectly.Since zoom has only http version of clicknupload, uploads cannot be done.Please add the https version of clicknupload.org to the list.Several filehosts also work in the same way.