private void AddAttachment(string itemId, string fileName, byte[] fileContent) { var binding = new BasicHttpBinding(BasicHttpSecurityMode.Transport); binding.Security.Transport.ClientCredentialType = HttpClientCredentialType.Ntlm; var listsSvc = new ListServices.ListsSoapClient(binding, new EndpointAddress(site + "/_vti_bin/Lists.asmx")); listsSvc.ClientCredentials.Windows.AllowedImpersonationLevel = TokenImpersonationLevel.Impersonation; listsSvc.ClientCredentials.Windows.ClientCredential = CredentialCache.DefaultNetworkCredentials; listsSvc.AddAttachment(listName, itemId, fileName, fileContent); }