mldonkey: 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/bin/mldonkey - from package: mldonkey-server

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