mpy.mpich2: 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/lib/debug/usr/lib/yorick/bin/mpy.mpich2 - from package: yorick-dbg
/usr/bin/mpy.mpich2 - from package: yorick-mpy-mpich2
/usr/lib/yorick/bin/mpy.mpich2 - from package: yorick-mpy-mpich2

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

Error in other languages:
mpy.mpich2: bevel nie gevind nie
mpy.mpich2: comandă negăsită
mpy.mpich2: comando não encontrado
mpy.mpich2: commande introuvable
mpy.mpich2: command not found
mpy.mpich2: käsku ei ole
mpy.mpich2: không tìm thấy lệnh
mpy.mpich2: komanda nerasta
mpy.mpich2: Kommando nicht gefunden.
mpy.mpich2: kommandot finns inte
mpy.mpich2: komut yok
mpy.mpich2: nie znaleziono polecenia
mpy.mpich2: níor aimsíodh an t-ordú
mpy.mpich2: no se encontró la orden
mpy.mpich2: no s'ha trobat l'ordre
mpy.mpich2: opdracht niet gevonden
mpy.mpich2: parancs nem található
mpy.mpich2: perintah tidak ditemukan
mpy.mpich2: príkaz nenájdený
mpy.mpich2: příkaz nenalezen
mpy.mpich2: команда не найдена
mpy.mpich2: командата не е открита
mpy.mpich2: 命令找不到
mpy.mpich2: コマンドが見つかりません