Exchange 2013 and Outlook Anywhere Problems

Hello, 

I have an Exchange 2013 Installation with 2 CAS , 2 MBX and LNB infront. Mailfow working perfect , OWA the same. From internal and from external. My problem is with the Outlook Anywhere.

I use testconnectivity website from microsoft and it passes all tests except the last one. The error is

Testing HTTP Authentication Methods for URL https://mail.domain.net/rpc/rpcproxy.dll?c738e8d9-40c7-4b18-a128-f1a95f43ae3a@domain.net:6002.
	The HTTP authentication test failed.
	Additional Details   A Web exception occurred because an HTTP 501 - NotImplemented response was received from Unknown. Headers received: Pragma: no-cache Content-Length: 29 Cache-Control: no-cache,no-store Content-Type: text/html Expires: now Elapsed Time: 615 ms.

Any ideas ?

Thanks