aa-update-browser: 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/sbin/aa-update-browser - from package: apparmor-utils

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

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