python2.6-preprocess: 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/python2.6-preprocess - from package: python2-preprocess

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

Error in other languages:
python2.6-preprocess: bevel nie gevind nie
python2.6-preprocess: comandă negăsită
python2.6-preprocess: comando não encontrado
python2.6-preprocess: commande introuvable
python2.6-preprocess: command not found
python2.6-preprocess: käsku ei ole
python2.6-preprocess: không tìm thấy lệnh
python2.6-preprocess: komanda nerasta
python2.6-preprocess: Kommando nicht gefunden.
python2.6-preprocess: kommandot finns inte
python2.6-preprocess: komut yok
python2.6-preprocess: nie znaleziono polecenia
python2.6-preprocess: níor aimsíodh an t-ordú
python2.6-preprocess: no se encontró la orden
python2.6-preprocess: no s'ha trobat l'ordre
python2.6-preprocess: opdracht niet gevonden
python2.6-preprocess: parancs nem található
python2.6-preprocess: perintah tidak ditemukan
python2.6-preprocess: príkaz nenájdený
python2.6-preprocess: příkaz nenalezen
python2.6-preprocess: команда не найдена
python2.6-preprocess: командата не е открита
python2.6-preprocess: 命令找不到
python2.6-preprocess: コマンドが見つかりません