twill-sh: 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/twill-sh - from package: python-twill

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

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