muffin-window-demo: 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/muffin-window-demo - from package: muffin

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

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