convert-ly: 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/convert-ly - from package: lilypond

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

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