I have a wcf client/server application that I'm trying to get deployed at a client location. I believe it's a cross-domain issue, as we've deployed it successfully on the same computer. I'm currently using basichttpbinding and a custombinding that just uses Soap1.2: if (!useBasic) { CustomBinding binding = new CustomBinding(); TextMessageEncodingBindingElement encoding = new TextMessageEncodingBindingElement(MessageVersion.Soap12, System.Text.Encoding.UTF8); HttpTransportBindingElement transport = new HttpTransportBindingElement(); transport.MaxReceivedMessageSize = BindingConstants.MaxStringContentLength; binding.Elements.Add(encoding); binding.Elements.Add(transport); return binding; } else { BasicHttpBinding binding = new BasicHttpBinding(); binding.MaxReceivedMessageSize = BindingConstants.MaxStringContentLength; return binding; } However the client tells me that they get an error "SOAP security negotiation with 'XXXXXXXXXXXX' for target 'XXXXXXXXXXX' failed. See inner exception for details." Now I haven't gotten the inner exceptions yet, but everything I research online tells me that BasicHttpBinding should fix this, however they tell me they are using BasicHttpBinding. Is this error possible with BasicHttpBinding like how I have mine set up above? Also, when I check my BasicHttpBinding.Security.Message.ClientCredentialType, it says UserName. Does this even matter if my Security.Mode is "None"? Thanks.