(quoted from email sent by Dr. Francesco Iannone)
The last version of NX NOMACHINE
(v.6.x) doesn¹t support freeNX login anymore.
Therefore you must download the NX client version 5.x available for the
following platforms:
Linux Centos 7
Linux Debian
MAC-OSX 10.7 or later
Windows 64 bit 7 or later.
The download service is available at wiki site at url:
https://wiki.eufus.eu/doku.php?id=nx_remote_conn