acknowledge.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/acknowledge.cgi - from package: xymon

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

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