convert.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 CentOS possible default full paths are:

/usr/lib/mailman/bin/convert.py - from package: mailman

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/lib/mailman/bin/convert.py - from package: mailman

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

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