mpimsg: 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/mpimsg - from package: lam-runtime

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

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