ESX Hosts Disconnecting After Upgrade to vSphere 4.1

When you upgrade to vSphere 4.1 your hosts might start disconnecting from your vCenter Server with the following error message: A general system error occurred: internal error: vmodl.fault.HostCommunication.  Restarting the management agents does not resolve the error, nor does rebooting the host.  This VMware KB points to name resolution issues, but that is not at fault here.  The issue is vCenter Server cannot manage an ESX 4.1 host.

Workaround / Solution

Currently there are two solutions available:

1. Upgrade your vCenter Server to version 4.1.  (Once you've upgraded you'll have to remove the hosts from your inventory and re-add it - simply reconnecting didn't work in my case)
2. Downgrade your ESX hosts to version 4

Strangely enough I could not find this documented anywhere on the VMware Knowledge Base, even though it seems to be a pretty widely reported problem.