aa-exec: 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-exec - from package: apparmor

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

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