mason_convert0.6: 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/bin/mason_convert0.6 - from package: perl-HTML-Mason

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

Error in other languages:
mason_convert0.6: bevel nie gevind nie
mason_convert0.6: comandă negăsită
mason_convert0.6: comando não encontrado
mason_convert0.6: commande introuvable
mason_convert0.6: command not found
mason_convert0.6: käsku ei ole
mason_convert0.6: không tìm thấy lệnh
mason_convert0.6: komanda nerasta
mason_convert0.6: Kommando nicht gefunden.
mason_convert0.6: kommandot finns inte
mason_convert0.6: komut yok
mason_convert0.6: nie znaleziono polecenia
mason_convert0.6: níor aimsíodh an t-ordú
mason_convert0.6: no se encontró la orden
mason_convert0.6: no s'ha trobat l'ordre
mason_convert0.6: opdracht niet gevonden
mason_convert0.6: parancs nem található
mason_convert0.6: perintah tidak ditemukan
mason_convert0.6: príkaz nenájdený
mason_convert0.6: příkaz nenalezen
mason_convert0.6: команда не найдена
mason_convert0.6: командата не е открита
mason_convert0.6: 命令找不到
mason_convert0.6: コマンドが見つかりません