njb-play: 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/njb-play - from package: libnjb-tools

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

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