nat-traverse: 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/nat-traverse - from package: nat-traverse

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

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