That's an older build (we've been on 90145 for at least two
weeks). Have you already contacted Support? They'd probably
recommend you apply the latest hotfix to the server. If all of your
managed machines are having the same problem, it's most likely the
server that's failing to communicate (versus the agent stopping or
erroring-out on all of your managed machines) but still it would be
worth looking at the Windows event logs to see if the Agent service is
terminating and if there's an associated error code you can
reference. Could there be a firewall rule in place that's blocking
communication between the Agents and the server? I've seen that
with our McAfee enterprise firewall in the past.
On the server, you
should also check the Windows event logs for errors that might
explain the lack of communication with the Agents. Also check its
firewall logs for blocked communication with the Agents. Hope some of
that helps.