gnome-falling-blocks: 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-falling-blocks - from package: gnome-games-extra

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

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