twill-fork: 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/twill-fork - from package: python-twill

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