I just downloaded the 16.3 install to my desktop using Firefix following the links that I provided, but of course, I am inside the Cadence network. I will try again tonight from home.
Are you actualy navigating to the link, or just directly trying to ftp it with the link you provided?
If I try the ftp portion of your link, and authenticate with my credentials, I get a 550 error:
550 /home/xxxxx/files/allegro/allegroviewers/files/allegro_free_viewer_16-3.exe: No such file or directory