lighty-enable-mod: 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/sbin/lighty-enable-mod - from package: lighttpd

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

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