If you just right click and remove node in the console then they will reconnect in 2 minutes. You need to do an uninstall of the agent either via Add/Remove programs or the Remote Agent Uninstaller.
Oh, missed that part. I have seen where someone clones a machine that has the agent installed and it shows up as the original machine.
You could go to the ip address listed to see what that machine actually is called. Maybe it has the wrong name or somehow thinks it is a different machine.
All else fails you can call support to help them work through this with you.
The servers have been removed from the network and decommissioned(powered down, removed network connection, removed HD and Memory, and destroyed).
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