fvwm-crystal.mplayer-wrapper: 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/fvwm-crystal.mplayer-wrapper - from package: fvwm-crystal

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

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