mtpaint: 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/mtpaint - from package: mtpaint

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

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