gnome-wm: 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-wm - from package: gnome-session

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

On Debian possible default full paths are:

/usr/bin/gnome-wm - from package: gnome-session-flashback

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

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