udp2file: 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/udp2file - from package: ion

You may install the required package with command apt-get install {package}
Error in other languages:
udp2file: bevel nie gevind nie
udp2file: comandă negăsită
udp2file: comando não encontrado
udp2file: commande introuvable
udp2file: command not found
udp2file: käsku ei ole
udp2file: không tìm thấy lệnh
udp2file: komanda nerasta
udp2file: Kommando nicht gefunden.
udp2file: kommandot finns inte
udp2file: komut yok
udp2file: nie znaleziono polecenia
udp2file: níor aimsíodh an t-ordú
udp2file: no se encontró la orden
udp2file: no s'ha trobat l'ordre
udp2file: opdracht niet gevonden
udp2file: parancs nem található
udp2file: perintah tidak ditemukan
udp2file: príkaz nenájdený
udp2file: příkaz nenalezen
udp2file: команда не найдена
udp2file: командата не е открита
udp2file: 命令找不到
udp2file: コマンドが見つかりません