prepop.pl: 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/popularity-contest/examples/bin/prepop.pl - from package: popularity-contest

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

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