nxclient: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On CentOS possible default full paths are:

/usr/bin/nxclient - from package: opennx

You may install the required package with command yum install {package}

Error in other languages:
nxclient: bevel nie gevind nie
nxclient: comandă negăsită
nxclient: comando não encontrado
nxclient: commande introuvable
nxclient: command not found
nxclient: käsku ei ole
nxclient: không tìm thấy lệnh
nxclient: komanda nerasta
nxclient: Kommando nicht gefunden.
nxclient: kommandot finns inte
nxclient: komut yok
nxclient: nie znaleziono polecenia
nxclient: níor aimsíodh an t-ordú
nxclient: no se encontró la orden
nxclient: no s'ha trobat l'ordre
nxclient: opdracht niet gevonden
nxclient: parancs nem található
nxclient: perintah tidak ditemukan
nxclient: príkaz nenájdený
nxclient: příkaz nenalezen
nxclient: команда не найдена
nxclient: командата не е открита
nxclient: 命令找不到
nxclient: コマンドが見つかりません