notify-4.1: command not found

Have You tried accessing the binary with the full path?

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:

/var/spool/hylafax/bin/notify-4.1 - from package: hylafax-server

You may install the required package with command apt-get install {package}
Error in other languages:
notify-4.1: bevel nie gevind nie
notify-4.1: comandă negăsită
notify-4.1: comando não encontrado
notify-4.1: commande introuvable
notify-4.1: command not found
notify-4.1: käsku ei ole
notify-4.1: không tìm thấy lệnh
notify-4.1: komanda nerasta
notify-4.1: Kommando nicht gefunden.
notify-4.1: kommandot finns inte
notify-4.1: komut yok
notify-4.1: nie znaleziono polecenia
notify-4.1: níor aimsíodh an t-ordú
notify-4.1: no se encontró la orden
notify-4.1: no s'ha trobat l'ordre
notify-4.1: opdracht niet gevonden
notify-4.1: parancs nem található
notify-4.1: perintah tidak ditemukan
notify-4.1: príkaz nenájdený
notify-4.1: příkaz nenalezen
notify-4.1: команда не найдена
notify-4.1: командата не е открита
notify-4.1: 命令找不到
notify-4.1: コマンドが見つかりません