xprep: 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/xprep - from package: xrootd-client

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

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