bt-agent: 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/bt-agent - from package: bluez-tools

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

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