Sample-NiUserTracker: 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 Debian possible default full paths are:

/usr/bin/Sample-NiUserTracker - from package: openni-utils

You may install the required package with command apt-get install {package}

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