"The type TraceWriter must derive from ITraceWriter" after upgrading to Web API 2

Question

We have a custom Web API ITraceWriter implementation named TraceWriter, registered as a service in the usual way in Application_Start.

After upgrading the Web API project to Web API 2, an HttpException is thrown in Application_Start:

The type TraceWriter must derive from ITraceWriter.
Parameter name: service
   at System.Web.Http.Controllers.ServicesContainer.Replace(Type serviceType, Object service)

Of course, the TraceWriter actually is deriving from ITraceWriter, so what is the problem?

Answer 1

The TraceWriter implementation was located in a different project, which still referenced System.Web.Http, Version=4.0.0.0. Installing the latest Microsoft.AspNet.WebApi.Core package in this project solved the problem.