mkbimage: 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/mkbimage - from package: grub-legacy

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

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