mhgui: 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/mhgui - from package: congruity

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

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