qb-blackbox: 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/sbin/qb-blackbox - from package: libqb

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

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