sb_bnserver: 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/sb_bnserver - from package: spambayes

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

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