Unhandled fault exception occured on calling Project Server PSI

MS Project Server 2010 has been working fine .But when i call it throug PSI unexpected error occured.

My Code snipped is attached here with. I have tried to call PSI in both ways as Web reference and as Service Reference

With WebReference

  WSProject.ProjectDataSet _pds = new MSP2010FormApp.WSProject.ProjectDataSet();
          
                string _url = "http://kovair-virsrv3:11111/Proj/_vti_bin/PSI/Project.asmx";
                WSProject.Project _proj = new MSP2010FormApp.WSProject.Project();
                _proj.PreAuthenticate = true;
                _proj.Url = _url;
                _proj.Credentials = new NetworkCredential(_uName, _passWord, _domain);
           
                _pds = _proj.ReadProjectList();

Exception

Message :Unhandled Communication Fault occurred

StackStace:

   at System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall)
   at System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String methodName, Object[] parameters)

With Service Reference

 WSProjectSvc.ProjectDataSet _projDataset= new MSP2010FormApp.WSProjectSvc.ProjectDataSet();
                string _url = "http://kovair-virsrv3:11111/Proj/_vti_bin/PSI/ProjectServer.svc";
                _projDataset=PopulateData(_projDataset, "ProjectServiceTest2010",true);
                WSProjectSvc.ProjectClient _projClient = new MSP2010FormApp.WSProjectSvc.ProjectClient("BasicHttpBinding_Project1");
              
                _projClient.ClientCredentials.Windows.ClientCredential = new NetworkCredential(_uName, _passWord, _domain);
           
                _projDataset = _projClient.ReadProjectList();

Exception

Message :Unhandled Communication Fault occurred

Stack Stace

.ServiceChannel.HandleReply(ProxyOperationRuntime operation, ProxyRpc& rpc)
   at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs, TimeSpan timeout)
   at System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs)
   at System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage methodCall, ProxyOperationRuntime operation)
   at System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message)

Exception rethrown at [0]:
   at System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage reqMsg, IMessage retMsg)
   at System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData, Int32 type)

ULS Log Entry:

System.ArgumentNullException: Value cannot be null.  Parameter name: account     at Microsoft.Office.Project.Server.ClaimsHelper.ConvertAccountFormat(String account)     at Microsoft.Office.Project.Server.AuthenticationHelper.AuthenticateUserByName(String userName, Guid siteId)    7242eb55-ca93-43ab-8f02-9d450c684d61

I have tried  to pick the project list from Power shell script also,but the error is same.

My project Server is installed in virtual machine.

Any suggessions for where to look would be appreciated

Thank You