convert.pyc: 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.pyc - from package: mailman

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

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