hexgplc-iso: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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/hexgplc-iso - from package: gprolog

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