gpk-dbus-service: 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/gpk-dbus-service - from package: gnome-packagekit-session

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

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