Thanks for the quick reply.
I've had a look in logs you pointed me too and can see when I browse "All Books" from the non autenticaed site there is a POST logged that is missing from log from the autenticated site. (extract from logs attached)
I'm confused as to why this should be as I thought permissions were inherited.
I dont have a great knowledge of IIS and there is probably some subtelty I'm missing, perhaps around the URL Rewrite rules and ASPX as I'm seeing the following message when I monitor traffic in Fiddler -
I'd be grateful for any advise anbody can offer.