sb_server: command not found

Have You tried accessing the binary with the full path?

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH

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_server - from package: spambayes

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