[Xymon] trimhistory and "No events received in the last 240 minutes"

Hi,

Since I launched this command "./trimhistory --cutoff=date +%s --date="1 Feb 2011" --drop --dropsvcs --droplogs --progress" I don't have anymore any event displayed in the "Non-green systems" page : "No events received in the last 240 minutes" and "No events acknowledged in the last 240 minutes"

Anyones knows why ?

Thanks