Windows Server Failover Cluster Firewall Validation generates an error: "An item with the same key has already been added"


When you run the Validate a Configuration wizard for Windows Server 2008 Failover Cluster, you may receive the following error:

"An error occurred while executing the test.  There was an error verifying the firewall configuration.  An item with the same key has already been added."


This error is reported if any network adapters have the same Globally Unique Identifier (GUID) across any nodes in the cluster.  This can be determined by running the following WMI query on each node in the cluster and comparing the results -

For example, from inside PowerShell, run: - Get-WMIObject Win32_NetworkAdapter | fl Name,Guid

A sample output for an adapter would look like this -

Name : Intel(R) PRO/1000 MT Desktop Adapter
GUID : {7488FB48-851A-40B6-AB47-1EA7408C762F}

Note This scenario typically occurs if an operating system image is being used to deploy cluster nodes and that image was not correctly prepared for deployment by running sysprep.


To resolve this issue the network interface GUID's on each of the nodes must be unique. One node can be left unchanged. But the following process must be performed against the remaining nodes.

  1. Download and then install the latest version of the network adapter driver on the computer.
  2. Click Start, click Run, type regedit, and then click OK.
  3. Locate and then delete the following registry subkey:
  4. If your server is a domain controller, go to step 5. If your server is not a domain controller, delete the following registry subkeys:
               HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip\Parameters\Adapters\ {GUID}
  5. Click Start, click Run, type sysdm.cpl, and then click OK.
  6. In the Systems Properties dialog box, click the Hardware tab, and then click Device Manager.
  7. In Device Manager, expand Network adapters, right-click the network adapter that you want, and then click Uninstall.
  8. Restart the computer.

To verify that the network interface GUID was updated, use one of the following methods.

Method 1: Perform the following:

Get-WMIObject Win32_NetworkAdapter | fl Name,Guid

Method 2: Run Failover Cluster's Validate a Configuration wizard, and make sure that the error does not occur.