If this error is happening with Web API then below is the reason

Usually App_Start/WebApiConfig contains route as

config.Routes.MapHttpRoute("DefaultApi", "api/{controller}/{id}", new { id = RouteParameter.Optional });

So change the above configuration to

config.Routes.MapHttpRoute("DefaultApi", "api/{controller}/{action}/{id}", new { id = RouteParameter.Optional });

Happing Kooding… !