Extending a cluster doesn't do anything

[Tim11]

So I have a 7-node cluster and am trying to add a node to it. I clicked Extend Cluster and then pasted the public DNS name of the new node in a box as you see

I accepted the database setup and re-entered the database administrator password

I then re-chose the private key and verified the settings 

I clicked next and say this

which is just my 7 original nodes with no mention of the new one. If I click Install, it goes right back to the main installer page without doing anything.  What did I do wrong? Should it be important the cluster has MEP 6.4.0

thanks,

Tim

[Tim11]

UPDATE: I made a new cluster with 11 nodes and extending the cluster worked fine. Don't know what it is about the number 7