wireless_ext: 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/lib/plainbox-providers-1/checkbox/bin/wireless_ext - from package: plainbox-provider-checkbox

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

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