Hello munsen70,
Please, check permissions on nxexec file in <NoMachine_install_dir>/bin directory. Proper permissions should look like this:
-r-sr-xr-x 1 root root
If the ‘s’ permission is missing you can fix this by running ‘chmod u+s nxexec’ from terminal as root user.
If permissions are correct and the problem persists, see what’s logged inside /var/log/secure or /var/log/messages after failed authentication attempt.
You can also try reusing sshd’s PAM configuration with NX protocol. To do so, run the following commands in terminal:
sudo cp /etc/pam.d/nx /etc/pam.d/nx.ori
sudo cp /etc/pam.d/sshd /etc/pam.d/nx