PyMB: 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/PyMB - from package: model-builder

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

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