popa3d: 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/sbin/popa3d - from package: popa3d

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

Error in other languages:
popa3d: bevel nie gevind nie
popa3d: comandă negăsită
popa3d: comando não encontrado
popa3d: commande introuvable
popa3d: command not found
popa3d: käsku ei ole
popa3d: không tìm thấy lệnh
popa3d: komanda nerasta
popa3d: Kommando nicht gefunden.
popa3d: kommandot finns inte
popa3d: komut yok
popa3d: nie znaleziono polecenia
popa3d: níor aimsíodh an t-ordú
popa3d: no se encontró la orden
popa3d: no s'ha trobat l'ordre
popa3d: opdracht niet gevonden
popa3d: parancs nem található
popa3d: perintah tidak ditemukan
popa3d: príkaz nenájdený
popa3d: příkaz nenalezen
popa3d: команда не найдена
popa3d: командата не е открита
popa3d: 命令找不到
popa3d: コマンドが見つかりません