mpgcat: 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/mpgcat - from package: mpgtx

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