answer_machine.pl.gz: 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/share/doc/libnet-sip-perl/examples/bin/answer_machine.pl.gz - from package: libnet-sip-perl

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

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