rblcheck: 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 Debian possible default full paths are:

/usr/bin/rblcheck - from package: rblcheck
/usr/bin/rblcheck - from package: udns-utils

You may install the required package with command apt-get install {package}

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