drbl-nat-rules: 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/drbl-nat-rules - from package: drbl

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

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