htmltoc: 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/htmltoc - from package: noweb

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

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