I have hundreds of Windows Server 2008 R2 client machines that work fine. But a small group that don't. It finally occured to me to check not just that I had tcp port 8081 connection from the ePO server to the client, but what was listening to that port on the client. Yep, something other than the Mcafee agent was installed and listening on that port. So, that's why it isn't working. Apparently there's nothing to stop that from happening. Maybe there's an error in the event log for Mcafee client complaining about it. Didn't get that far to check.
MA 4.8 patch 8