Organization Service call fails for defaultnetworkcredentials in crm 2011 IFD - https://companyname:444/XRMServices/2011/Organization.svc

Hi All,
Could you please help me to resolve the below issue?

I am getting SOAP Negotiation Exception in Organization Service call when using DefaultNetworkCredentials. But if i am using the Username and Password, it works fine. Exactly in "WhoAmIResponse response = (WhoAmIResponse)_service.Execute(new WhoAmIRequest());" from the code snippet.

Code:
-----
Uri organizationUriIFD = new Uri("Organization URL");

ClientCredentials credentials = new ClientCredentials();
credentials.Windows.ClientCredential = System.Net.CredentialCache.DefaultNetworkCredentials;

IServiceConfiguration<IOrganizationService> config = ServiceConfigurationFactory.CreateConfiguration<IOrganizationService>(organizationUriIFD);         

using (Microsoft.Xrm.Sdk.Client.OrganizationServiceProxy _serviceProxy = new OrganizationServiceProxy(config, credentials))
{                              
_serviceProxy.ServiceConfiguration.CurrentServiceEndpoint.Behaviors.Add(new ProxyTypesBehavior());
IOrganizationService _service = (IOrganizationService)_serviceProxy;
OrganizationServiceContext orgContext = new OrganizationServiceContext(_serviceProxy);
WhoAmIResponse response = (WhoAmIResponse)_service.Execute(new WhoAmIRequest());
return _service;
} 

Exception:
----------
SOAP security negotiation with 'https://...../adfs/services/trust/13/kerberosmixed' for target 'https://.../adfs/services/trust/13/kerberosmixed' failed. See inner exception for more details. ---> System.IdentityModel.Tokens.SecurityTokenValidationException: The NetworkCredentials provided were unable to create a Kerberos credential, see inner exception for details. ---> System.IdentityModel.Tokens.SecurityTokenException: InitializeSecurityContent failed. Ensure the service principal name is correct. ---> System.ComponentModel.Win32Exception: No authority could be contacted for authentication

Thanks in advance.

--Siva