SYMPTOM:
Trying to add a node to a cluster in Strategy Intelligence Server 9.x and 10.x using the Cluster Manager in Strategy Developer fails with the following error:

Failed to join cluster:Server "Servername" is not found or reachable.
CAUSE:
This is because Strategy Intelligence Server 9.x and 10.x instances on the two machines have been configured to run on different port numbers. Currently, Strategy Intelligence Server is designed to cluster only when running on the same port number.
ACTION:
An enhancement request has been logged for the ability to cluster Strategy Intelligence Servers on different port numbers.
Strategy will continue to investigate and post updates as soon as they are available.
WORKAROUND:
Configure Strategy Intelligence Server 9.x and 10.x to use the same port in all the nodes to be clustered.