This is correct Robert, however there is another case too with some aircraft. These use panels from the FSNORDIC web site (which IMHO is a very interesting site BTW).
It looks like AFTER the EHM site was built, policy at FSNORDIC has changed and does no longer allow links directly to specific pages or items on their site. For these reasons these links from EHM pages no longer work.
What to do? If you get an error when clicking the "Panel" link in the EHM page, AND the link points to a FSNORDIC page (which in MSIE is shown on the status bar), then go to
http://www.fsnordic.net, look for that specific panel and download it.
Alternatively, you could note the file name in the original link and look for that specific file.
Hope this helps
Andrei