identify_paired_differences.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/identify_paired_differences.py - from package: qiime

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

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