sb_bnfilter: 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_bnfilter - from package: spambayes

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

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