mdm.screen: 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/mdm.screen - from package: mdm

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

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