This is driving me insane, Outlook Anywhere issue Exchange 2013

I have spent so much time on this, it's not funny.

Exchange Connectivity test

	Attempting to ping RPC proxy mail.contoso.co.nz.
 	RPC Proxy can't be pinged.
	Additional Details
 	A Web exception occurred because an HTTP 404 - NotFound response was received from Unknown.

DAG and CAS are on seperate servers. Everything is forwarded to CAS.

OWA etc all working fine. External Outlook over RPC does not work, obviously.

External/Internal URLs are the same. basic authentication on external, ntlm on internal, IIS has basic, ntlm and negotiate.

I had Exchange 2013 RTM, upgraded to CU1, still have same issues.

Please give me a hand. Next step is Microsoft Support.