handler.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/python2.6/site-packages/viewvc/bin/mod_python/handler.py - from package: viewvc

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

On Debian possible default full paths are:

/usr/share/gforge/www/scm/viewvc/bin/mod_python/handler.py - from package: gforge-web-apache2

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

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