Could you confirm that you can log in with no problems to the same host using ssh? If so, please send us the output of the following command (ran as root):
grep -R nxexec /var/log/*
Could you also compress the /usr/NX/var/log and /etc/pam.d directories and send them to us? If they are too large to attach to forum, please send us an e-mail on issues [at] nomachine [dot] com.