mocp: 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/mocp - from package: moc

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

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