xymoncgimsg.cgi: 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
/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/xymoncgimsg.cgi - from package: xymon

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