mpgjoin: 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/mpgjoin - from package: mpgtx

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

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