trimhistory and "No events received in the last 240 minutes"

list L.M.J
Mon, 10 Jun 2013 17:21:44 +0200
Message-Id: <user-151b07df43ba@xymon.invalid>

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