version-mixing: 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/lib64/piglit/bin/version-mixing - from package: piglit

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

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