pcl_openni_change_viewer: 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/pcl_openni_change_viewer - from package: pcl-tools

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

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