mfplain: 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/mfplain - from package: texlive-binaries

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

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