upnp-inspector: 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/upnp-inspector - from package: upnp-inspector

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

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