There are three types of message encodings that come with WCF: text, binary, and MTOM. Text is the traditional way of encoding an XML document; MTOM is an interoperable way to create messages with attachments; and binary is an optimized format. The binary message encoder requires you to use SOAP 1.2 and any version of message addressing. Validation for the message encoder checks that you are using SOAP 1.2. The validation doesn't check to make sure that you have some kind of message addressing, so if you are using AddressingVersion.None, then that won't show up as an error until you try to send a message. It may be difficult to figure out the cause of the error because the resulting message looks invalid and the connection just gets refused. If you are capturing all of the exceptions that occur though, you should see something that looks like one of these stack traces when you have an invalid configuration. The stack trace when using HTTP is going to look like: System.ServiceModel.Channels.BinaryMessageEncoderFactory.BinaryMessageEncoder.ReadMessage + 0x299 bytes System.ServiceModel.Channels.HttpInput.DecodeBufferedMessage + 0x56 bytes System.ServiceModel.Channels.HttpInput.ReadBufferedMessage + 0x7e bytes System.ServiceModel.Channels.HttpInput.ParseIncomingMessage + 0x9e bytes System.ServiceModel.Channels.HttpRequestContext.CreateMessage + 0x2e bytes System.ServiceModel.Channels.HttpChannelListener.HttpContextReceived + 0x99 bytes System.ServiceModel.Channels.SharedHttpTransportManager.OnGetContextCore + 0x231 bytes System.ServiceModel.Channels.SharedHttpTransportManager.OnGetContext + 0x1e bytes System.ServiceModel.Diagnostics.Utility.AsyncThunk.UnhandledExceptionFrame + 0x28 bytes System.Net.LazyAsyncResult.Complete + 0x7f bytes System.Net.LazyAsyncResult.ProtectedInvokeCallback + 0x8b bytes System.Net.ListenerAsyncResult.WaitCallback + 0x22a bytes System.Threading._IOCompletionCallback.PerformIOCompletionCallback + 0x68 bytes The stack trace when using TCP or named pipes is going to look like: System.ServiceModel.Channels.TransportOutputChannel.TransportOutputChannel + 0x8b bytes System.ServiceModel.Channels.FramingDuplexSessionChannel.FramingDuplexSessionChannel + 0x4f bytes System.ServiceModel.Channels.FramingDuplexSessionChannel.FramingDuplexSessionChannel + 0x38 bytes System.ServiceModel.Channels.ServerSessionPreambleConnectionReader.ServerFramingDuplexSessionChannel.ServerFramingDuplexSessionChannel + 0x29 bytes System.ServiceModel.Channels.TcpDuplexChannelListener.System.ServiceModel.Channels.ISessionPreambleHandler.HandleServerSessionPreamble Read More...