Ensure that HttpConfiguration.EnsureInitialized()

See @gentiane's answer below for the correct way to handle this now.

At the end of the Application_Start method in Global.Asax.cs try adding:-

GlobalConfiguration.Configuration.EnsureInitialized(); 

If you do it at the end of Application_Start it will be too late, as WebApiConfig.Register has been called.

The best way to resolve this is to use new initialization method by replacing in Global.asax :

WebApiConfig.Register(GlobalConfiguration.Configuration);

by

GlobalConfiguration.Configure(WebApiConfig.Register);