poller_example.py: 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/lib/qiime/bin/poller_example.py - from package: qiime

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

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