ncftp3: 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/ncftp3 - from package: ncftp

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

Error in other languages:
ncftp3: bevel nie gevind nie
ncftp3: comandă negăsită
ncftp3: comando não encontrado
ncftp3: commande introuvable
ncftp3: command not found
ncftp3: käsku ei ole
ncftp3: không tìm thấy lệnh
ncftp3: komanda nerasta
ncftp3: Kommando nicht gefunden.
ncftp3: kommandot finns inte
ncftp3: komut yok
ncftp3: nie znaleziono polecenia
ncftp3: níor aimsíodh an t-ordú
ncftp3: no se encontró la orden
ncftp3: no s'ha trobat l'ordre
ncftp3: opdracht niet gevonden
ncftp3: parancs nem található
ncftp3: perintah tidak ditemukan
ncftp3: príkaz nenájdený
ncftp3: příkaz nenalezen
ncftp3: команда не найдена
ncftp3: командата не е открита
ncftp3: 命令找不到
ncftp3: コマンドが見つかりません