eventlog.cgi: 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/lib/xymon/server/bin/eventlog.cgi - from package: xymon

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

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