mathtex: 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/mathtex - from package: mathtex

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

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