HTTP authentication test failed in RPC/HTTP

HI 

I have setup NLB Cluster for 2 CAS Servers and DAG for 2 MBX Servers. These Server are Exchange 2013/windows 2012 VMs in HyperV.

Everything is working fine internally and externally. But when i am performing RPC/HTTP test in www.testexchangeconnectivity.com i am getting http authentication failed message there. I have also tested by changing the authentication to NTLM and Basic in outlook anywhere settings, But after that my credentials did not work to login in outlook. Please advise how to troubleshoot this problem.

Testing HTTP Authentication Methods for URL https://mail.domain.com/rpc/rpcproxy.dll?1550cfff-9bb0-4678-82f7-f342ebb1bed9@domain.com:6002.
	The HTTP authentication test failed.
	<label for="testSelectWizard_ctl12_ctl06_ctl06_tmmArrow">Tell me more about this issue and how to resolve it</label>
	Additional Details   Not all the required authentication methods were found. Methods Found: Negotiate Methods Required: NTLM