dtdparse: 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/dtdparse - from package: libsgml-dtdparse-perl

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

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