After reinstalling or upgrading NX Server it is possible that NX Clients will receive this message when trying to login:

NX> 202 Authenticating user: nx
NX> 208 Using auth method: publickey
NX> 204 Authentication failed.

This is most likely in the case where the administrator has replaced the default SSH keys used by NX with keys generated for their specific server as explained in the following Article:

https://www.nomachine.com/AR01C00126

During the reinstallation or upgrade process, setup replaces those specific keys with the default keys provided with NX Server.

When using server-specific SSH keys, we suggest the following  procedure for upgrading or reinstalling the server. Procedure is tailored for NX Server 3.5.0.

1) Stop access to he NX Server

# /usr/NX/bin/nxserver --stop
 

2) Inform users about the upgrade/reinstall operation

# /usrNX/bin/nxserver --broadcast "Your message here"
 

3) Terminate all running sessions

# /usr/NX/bin/nxserver --shutdown

4) Make a backup of your current NX installation and protect sensitive information that may be present inside the TAR archive by making the backup readable only by the 'root' user:

# cd /usr
# tar cvzpf /root/nx-BACKUP.tar.gz NX
# chmod 0600 /root/nx-BACKUP.tar.gz

5) Upgrade or reinstall NX Server 3.5.0 - you may reference instructions for that procedure in the NX Server Installation Instructions linked here: https://www.nomachine.com/DT12I00007

6) Restore the directories that contain your specific keys from the old installation:

# tar xzvpf /root/nx-BACKUP.tar.gz -C /usr NX/home/nx/.ssh
# tar xzvpf /root/nx-BACKUP.tar.gz -C /usr NX/share/keys

Your clients should now be able to reconnect to the NX Server using your specific keys.