gksu-properties: 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/gksu-properties - from package: libgksu2-0

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

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