set-default-pxe-img: 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/share/drbl/sbin/set-default-pxe-img - from package: drbl

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

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