natpmpc: 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/natpmpc - from package: libnatpmp

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

On Debian possible default full paths are:

/usr/bin/natpmpc - from package: natpmp-utils

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

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