IIS 6 Available certificates list
I believe you have a certificate of the wrong type the IIS certificate needs to authenticate the server to the client and therefore needs to have the key usage server authentication you indicate it has client authentication. Without more detail its hard to tell but thats what im reading from your text. IIS wont let you pick it as its not suitable is my suggestion.
Where other templates available from the CA, with Server Auth available?
What was the CA type?
Mark Sutton
http://www.blacktipconsulting.com