twoftpd-switch: 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/twoftpd-switch - from package: twoftpd

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

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