grub-macbless: 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/sbin/grub-macbless - from package: grub-common

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

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