domain based webservice connection problem

When I try to connect domain based  webservice from my system getting "The request failed with HTTP status 401: Unauthorized"  error .What could be the problem.
When i browse the service from browser(http://10.1.23.4/gss/myManagerService.asmx) i can see the service output but when i try to connect from my below programe getting 401 error.
Please advice me.

  MyService service= new MyService ();
        System.Net.CredentialCache cache = new System.Net.CredentialCache();
        cache.Add(new Uri("http://10.1.23.4/gss/myManagerService.asmx"), new    System.Net.NetworkCredential("muusername", "mypwd","mydomain"));
        service.Url = "http://10.1.23.4/gss/myManagerService.asmx";
        int cnt = 0;
        myrec[] records = new myrec[0];
                AccRecord oaccRecord = new AccRecord ();
              
                DateTime enddt = DateTime.Now;
                DateTime stdt = DateTime.Now.AddDays(-10);
                service.Credentials = cache;
                MessageBox.Show("service");
                records =service.ReadRecord(records , stdt, enddt);// here taking some time and throwing          401 eroor