You are connected to a server in a Lotus® Domino® cluster. That server stops responding, and as expected, Notes attempts to fail over to other servers in the cluster. However, a "Server not responding" error is returned for those servers even though they are functional.
This issue will occur if the cluster.ncf on your workstation does not contain information on the clustermates. For information on how the cluster.ncf gets created and populated, refer to the document titled: "When is cluster.ncf created by a Notes client or a Domino server?" (#1087756)