twoftpd-auth: 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-auth - from package: twoftpd

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

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