process_iseq.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/process_iseq.py - from package: qiime

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

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