Trying to add a service reference results in Bad Request (400) in one project, otherwise runs fine

Question 1

For the beginning you have to find an issue, I mean you need to know what happens on server side. You need to handler all error and log them.

Logging errors

    public class GlobalErrorHanler: IErrorHandler 
    {
        //to use log4net you have to have a proper configuration in you web/app.config
        private static readonly ILog Logger = LogManager.GetLogger(typeof (GlobalErrorHandler));

        public bool HandleError(Exception error)
        {
            //if you host your app on IIS you have to log using log4net for example
            Logger.Error("Error occurred on the service side", error);

            //Console.WriteLine(error.Message); 
            //Console.WriteLine(error.StackTrace);

            return false;
        }

        public void ProvideFault(Exception error, System.ServiceModel.Channels.MessageVersion version, ref System.ServiceModel.Channels.Message fault)
        {
            //you can provide you fault exception here
        }
    }

Then service behavior (inherits Attribute to add possibility to use it as an attribute on service implementation):

public class MyErrorHandlingBehavior : Attribute, IServiceBehavior
{

    public void AddBindingParameters(ServiceDescription serviceDescription, System.ServiceModel.ServiceHostBase serviceHostBase, System.Collections.ObjectModel.Collection<ServiceEndpoint> endpoints, System.ServiceModel.Channels.BindingParameterCollection bindingParameters)
    {
        return;
    }

    public void ApplyDispatchBehavior(ServiceDescription serviceDescription, System.ServiceModel.ServiceHostBase serviceHostBase)
    {
        foreach (ChannelDispatcher disp in serviceHostBase.ChannelDispatchers)
            disp.ErrorHandlers.Add(new GlobalErrorHanler());
    }

    public void Validate(ServiceDescription serviceDescription, System.ServiceModel.ServiceHostBase serviceHostBase)
    {        }
}

And extension element to use it in your config:

public class ErrorHandlerExtention: BehaviorExtensionElement
{

    public override Type BehaviorType
    {
        get { return typeof(MyErrorHandlingBehavior); }
    }

    protected override object CreateBehavior()
    {
        return new MyErrorHandlingBehavior();
    }
}

Then add to config file:

<system.serviceModel>
  <extensions>
    <behaviorExtensions>
      <!-- Extension.ErrorHandlerExtention: fully qualified class name, ArrayList: assebmly name-->
      <add name="errorHandler" type="Extension.ErrorHandlerExtention, Extensions"/>
    </behaviorExtensions>
  </extensions>

<behaviors>
  <serviceBehaviors>
    <behavior name="CalculatorServiceBehavior">
      <serviceMetadata httpGetEnabled="true"/>
      <serviceDebug includeExceptionDetailInFaults="False"/>

      <!-- the name of this element must be the same as in the section behaviorExtensions -->
      <errorHandler />

    </behavior>
  </serviceBehaviors>
</behaviors>

</system.serviceModel>

This will allow you to get an error. When you have an error get back to the forum.

Some more posts with this technique: Error 1, Error 2

Tracing:

To turn on tracing you have to add such lines to a config:

<system.diagnostics>
  <trace autoflush="true" />
  <sources>
    <source name="System.ServiceModel"
            switchValue="Information, ActivityTracing"
            propagateActivity="true">
      <listeners>
        <add name="log"
            type="System.Diagnostics.XmlWriterTraceListener"
            initializeData= "C:\traces.svclog" />
      </listeners>
    </source>
  </sources>
</system.diagnostics>

Tracing tool: Trace Viewer

Question 2

Cannot say what the problem is but here is some info to help you find the problem.

When you do "Add Service Reference" there is a http get Call that goes to the service. I am assuming that it is this Call that Returns http 400. You have a mex endpoint and httpgetenabled, missing these are the normal problems.

You can try Reading the wsdl using a browser and see if that Works.

Reasons could be:

Port 8000 is blocked
The IIS site is on a different port
You are Accessing the site using the machine name and the config uses local host
the binding is not enabled in iis for that port

Question 3

For anyone who is encountering similar issues without detailed error, I'll describe what my problem was about. In my Visual Studio project, I used a class similar to the following:

public class Info
{
  public string Key { get; set; }
  public string Value { get; set; }

  public Info(string key, string value)
  {
    this.Key = key;
    this.Value = value;
  }
}

The difference to the other project (which worked) is that this POCO has a constructor that takes parameters, thus doesn't provide a standard constructor without any arguments. But this is needed in order for Info objects to be serialized (I hope I use that term correctly here) and deserialized. So in order to make it work, either just add a standard constructor which may just do nothing, or (perhaps better) use the following instead:

[DataContract]
public class Info
{
  [DataMember]
  public string Key { get; set; }
  [DataMember]
  public string Value { get; set; }

  public Info(string key, string value)
  {
    this.Key = key;
    this.Value = value;
  }
}

I didn't think about the DataContract part before, because I didn't use any custom constructor and just initialized the objects like

Info info = new Info { Key = "a", Value = "b" };