nsctl: command not found

Have You tried accessing the binary with the full path?

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/nsctl - from package: l2tpns

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