WCF Metadata contains a reference that cannot be resolved

I received the same error while attempting to update an existing service reference. It turns out I had data contracts with the same name within the same namespace. Further investigation yielded the real error:

DataContract for type [redacted] cannot be added to DataContractSet since type '[redacted]' with the same data contract name 'DocumentInfo' in namespace '[redacted]' is already present and the contracts are not equivalent.

I changed the DataContract to provide a name for one of the classes.

[DataContract(Namespace = "urn:*[redacted]*:DataContracts", Name = "SC_DocumentInfo")]

I'm posting this here in case it might help someone with the same issue.

You are missing service configuration

<system.serviceModel>
  <services>
    <service name="WcfService_using_callbacks_via_tcp.Service1" 
      behaviorConfiguration="Behavior_Service1">
      <host>
        <baseAddresses>
          <add baseAddress="net.tcp://localhost:5050/Service1" />
        </baseAddresses>
      </host>
      <endpoint address="" contract="WcfService_using_callbacks_via_tcp.IService1"
         binding="netTcpBinding" bindingConfiguration="DuplexNetTcpBinding_IService1" />
      <endpoint address="mex" contract="IMetadataExchange" binding="mexTcpBindng" />
    </service>
  </services>
  ...
</system.serviceModel>

With this config you should not need to define base address in code.

I was getting the same error message and as it turned out, the issue was due to text within a comments block

<!-- comments included characters like à, ç and ã -->

After removing such characters from the commented block, everything works fine

Maybe it will be helpful for someone.

My issue was in a contract argument, and I discovered it with help of Event Viewer:

The operation [Name of method] either has a parameter or a return type that is attributed with MessageContractAttribute. In order to represent the request message using a Message Contract, the operation must have a single parameter attributed with MessageContractAttribute. In order to represent the response message using a Message Contract, the operation's return value must be a type that is attributed with MessageContractAttribute and the operation may not have any out or ref parameters.

So, if you appended more than one arguments, already having [MessageContract] argument, then you'll see error in question. Completely not obvious.