gnome-mplayer: 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/gnome-mplayer - from package: gnome-mplayer

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

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