mbchk: 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 CentOS possible default full paths are:

/usr/bin/mbchk - from package: grub

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/mbchk - from package: grub-legacy

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

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