muddleftpd: 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/muddleftpd - from package: muddleftpd

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

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