dislocker-bek: command not found

Have You tried accessing the binary with the full path?

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/dislocker-bek - from package: dislocker

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