supybot-adduser: 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 CentOS possible default full paths are:

/usr/bin/supybot-adduser - from package: supybot-gribble
/usr/bin/supybot-adduser - from package: supybot

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/supybot-adduser - from package: supybot

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

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