So I’ve seen this a couple times and I always forget how to handle it, so hopefully writing this down will help me remember for next time…

You are replacing some Remote Desktop Session Host (RDSH) with a newer server, and everything looks good-to-go. Back on your Remote Desktop Connection Broker (RDCB), you have Server Manager open, and you proceed to remove the old RDSH servers. Easy. You then go back to edit other properties in in your RDS deployment and – BAM – you get an error message that states:

The following servers in this deployment are not part of the server pool:
1. <Old.RDSH.ServerName>
The servers must be added to the server pool

Powershell to our rescue! On your RDCB, open up a PowerShell window as an Administrator. Run the command below.

PS C:\> Get-RDServer

This will return a list of all the Remote Desktop servers you have in RDCB as well as their installed roles. You should see your old, unwanted, RDSH server in that list. Next, we can enter the command below to remove our orphaned RDSH server.

PS C:\> Remove-RDServer Old.RDSH.ServerName RDS-RD-SERVER

This will remove the ‘RDS-RD-SERVER’ role. Now if you go back to your RDCB, and back to your deployment, everything should be back to normal. It is no longer expecting the “Old.RDSH.Server” to be a server that Server Manger manages. In fact, at this point you should be able to remove it as a managed server.

Note: RDS is a complicated beast. The above mentioned trick utilizing PowerShell has worked for me the couple times I’ve needed in my scenario. However, your mileage may vary depending on your environment.