Unable to Remove from Management Group

[WindowsRUs]

We are decommissioning multiple StoreVirtual systems. After deleting a cluster and then trying to remove systems from the management group, some systems failed with a network connectivity error. They no longer show the system name in the CMC, just the IP address. When attempting to expand the system this error is displayed: "Could not find storage system with serial number XX:XX:XX:XX:XX:XX." (serial number removed). One system shows offline even though it is up. How can I remove these failed systems from the management group? One cluster will remain in this management group.

Edit: It now shows this message at the console: "Cannot log in to the console because the storage system has not yet fully initialized. Wait a minute and try again."

[Fred Blum]

Which StoreVirtual system are you using? Never seen this on our a P4300 4 node system. Removing a node from the MG is routine before maintenace. 

Have you tried rebooting the affected nodes?

[WindowsRUs]

P4500 G2. One of the two nodes has been rebooted. It now shows the message mentioned in my edit in the original post.