dfg2ascii: 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
/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/dfg2ascii - from package: spass

You may install the required package with command apt-get install {package}
Error in other languages:
dfg2ascii: bevel nie gevind nie
dfg2ascii: comandă negăsită
dfg2ascii: comando não encontrado
dfg2ascii: commande introuvable
dfg2ascii: command not found
dfg2ascii: käsku ei ole
dfg2ascii: không tìm thấy lệnh
dfg2ascii: komanda nerasta
dfg2ascii: Kommando nicht gefunden.
dfg2ascii: kommandot finns inte
dfg2ascii: komut yok
dfg2ascii: nie znaleziono polecenia
dfg2ascii: níor aimsíodh an t-ordú
dfg2ascii: no se encontró la orden
dfg2ascii: no s'ha trobat l'ordre
dfg2ascii: opdracht niet gevonden
dfg2ascii: parancs nem található
dfg2ascii: perintah tidak ditemukan
dfg2ascii: príkaz nenájdený
dfg2ascii: příkaz nenalezen
dfg2ascii: команда не найдена
dfg2ascii: командата не е открита
dfg2ascii: 命令找不到
dfg2ascii: コマンドが見つかりません