I recently had to remove a node from my existing DAG. I had a four node cluster, and removed one DAG member. I removed it b/c I moved that VM from one virtual infrastructure to another, resulting in the MAC address changing. All other settings in the VM are the same, including the network config, except for the MAC changing on each nic. I figured that removing the node from the cluster, and then re-adding it would fix the changed MAC issue.
To do this, I moved all mailbox database copies off of the node, and then gracefully removed the node from the DAG. I then rebooted and tried to add the node back in, but it errors out each time with this error:
"An Active Manager operation failed. Error an error occurred while attempting a cluster operation. Error: Node [name] is already joined to a cluster..."
I verified with Failover Cluster Manager that the node in question was removed. It does not show up, nor do either of the two networks show up from that node (MAPI and DAG networks). I ran the cluster validation test, and all passed for this server to be placed back into cluster.
I have tried manually removing the Failover Cluster Feature and the Failover Cluster Manager. I then try the process again, and it fails. I have not changed the networking from when this node was participating in the DAG.