Cluster Firewall issue – An item with the same key has already been added.
When running a HA cluster verification you may get the following;
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 is typically because the NIC GUID is duplicated between cluster nodes.
This could be because servers were deployed from an image, or cloned. Personally I had this with a VMware deployed server from a Template.
Remove and re-add a new NIC (add the new one first to be sure) and re-validate 🙂