Can you post the agent log and mcscript.log from an affected machine? It's a bit unusual that they would all fail at the same time...
Okay, a couple of things spring to mind. Firstly - bizarre as it may sound - it doesn't look like this machine is running an update task? The only tasks that appear to be running are called "VirusScan Enterprise 8.7i Deployment [TC]" and "Collect Information [TC]" - I'm assuming that neither of these is an update task. Has someone disabled or removed the update task assigned to the affected machines?
Secondly - looks like the server may be having some load problems. The log mentions errors like this:
2010-08-13 10:00:01 i #3728 Agent ePO Server is busy
2010-08-13 10:00:01 i #3728 Agent Agent communication session closed
2010-08-13 10:00:01 I #3728 Agent Setting flag to force full properties on next ASCI
2010-08-13 10:00:01 I #3728 Agent Agent communication failed, result=-2403
2010-08-13 10:00:01 I #3728 Agent Exponential retry in 335 seconds, error=-2403(Server busy or reaches max concurrent download number)
Check the server.log on the epo server - are there any errors about max connections being reached, or possibly sequence numbers being rejected?
Looks like someone thought it would be a good idea to disable the update task the Server Group...
I shouldve checked this first, but your post prompted me to.
Someone is about to get an ear full.
Happens all the time
You still definitely should check the server.log for any errors though.