aptitude-robot-session: 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/aptitude-robot-session - from package: aptitude-robot

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

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