lighttpd-disable-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/lighttpd-disable-mod - from package: lighttpd

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

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