midi2ly: 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/midi2ly - from package: lilypond

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

Error in other languages:
midi2ly: bevel nie gevind nie
midi2ly: comandă negăsită
midi2ly: comando não encontrado
midi2ly: commande introuvable
midi2ly: command not found
midi2ly: käsku ei ole
midi2ly: không tìm thấy lệnh
midi2ly: komanda nerasta
midi2ly: Kommando nicht gefunden.
midi2ly: kommandot finns inte
midi2ly: komut yok
midi2ly: nie znaleziono polecenia
midi2ly: níor aimsíodh an t-ordú
midi2ly: no se encontró la orden
midi2ly: no s'ha trobat l'ordre
midi2ly: opdracht niet gevonden
midi2ly: parancs nem található
midi2ly: perintah tidak ditemukan
midi2ly: príkaz nenájdený
midi2ly: příkaz nenalezen
midi2ly: команда не найдена
midi2ly: командата не е открита
midi2ly: 命令找不到
midi2ly: コマンドが見つかりません