NiSimpleViewer: 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/NiSimpleViewer - from package: openni-examples

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

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