ncftp: 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 CentOS possible default full paths are:

/usr/bin/ncftp - from package: ncftp

You may install the required package with command yum install {package}

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