kdesu_stub: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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 CentOS possible default full paths are:

/usr/bin/kdesu_stub - from package: kdelibs3

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