Getting "Recursive collection data contract" when referencing a WCF service with a slightly complex method

Question

If I use only simple methods in my WCF service, everything works fine. However, if I include the following method, a problem occurs:

[OperationContract]
public List<KeyValuePair<string, string>> GetAllAccounts()
{
    return AccountBusiness.GetAllAccounts();
}

I get this error when referencing the service from another project:

Warning 5 Custom tool warning: Cannot import wsdl:portType Detail: An exception was thrown while running a WSDL import extension: System.ServiceModel.Description.DataContractSerializerMessageContractImporter Error: Type 'Newtonsoft.Json.Linq.JToken' is a recursive collection data contract which is not supported. Consider modifying the definition of collection 'Newtonsoft.Json.Linq.JToken' to remove references to itself. XPath to Error Source: //wsdl:definitions[@targetNamespace='http://tempuri.org']/wsdl:portType[@name='NodeService'] C:\inetpub\wwwroot\MyclientProject\Service References\NodeService\Reference.svcmap 1 1 MyClientNode

If I remove the method above, recompile and update the reference, then it works fine. But when I add the above method, I consistently get this warning.

One suggestion I found was to uninstall Visual Studio 2012 and repair Visual Studio 2010. I don't want to do that.

Another suggested to uncheck "Reuse types in all referenced assemblys", but this messes up the method signatures and is not usable.

Answer 1

As it turned out, the error was caused by the fact that I had a Microsoft Web API package installed from NuGet, which included Json.NET. After uninstalling this, it works fine.

This may be the answer for you - if not, look at which other packages you have installed (that you don't need) and remove them.