mkzftree: 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/mkzftree - from package: genisoimage

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

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