mp3fs: 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/mp3fs - from package: mp3fs

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

Error in other languages:
mp3fs: bevel nie gevind nie
mp3fs: comandă negăsită
mp3fs: comando não encontrado
mp3fs: commande introuvable
mp3fs: command not found
mp3fs: käsku ei ole
mp3fs: không tìm thấy lệnh
mp3fs: komanda nerasta
mp3fs: Kommando nicht gefunden.
mp3fs: kommandot finns inte
mp3fs: komut yok
mp3fs: nie znaleziono polecenia
mp3fs: níor aimsíodh an t-ordú
mp3fs: no se encontró la orden
mp3fs: no s'ha trobat l'ordre
mp3fs: opdracht niet gevonden
mp3fs: parancs nem található
mp3fs: perintah tidak ditemukan
mp3fs: príkaz nenájdený
mp3fs: příkaz nenalezen
mp3fs: команда не найдена
mp3fs: командата не е открита
mp3fs: 命令找不到
mp3fs: コマンドが見つかりません