gnome-screensaver-command: 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 CentOS possible default full paths are:

/usr/bin/gnome-screensaver-command - from package: gnome-screensaver

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/gnome-screensaver-command - from package: gnome-screensaver

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

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