kpolygon.kss: 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/kpolygon.kss - from package: kscreensaver

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

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