mkexfatfs: 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:

/sbin/mkexfatfs - from package: exfat-utils

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

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