dpkg-www-installer: 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/sbin/dpkg-www-installer - from package: dpkg-www

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