ndisgtk: 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/sbin/ndisgtk - from package: ndisgtk

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

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