mhfixmsg: 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/mh/mhfixmsg - from package: nmh

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

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