<Error> <Message>An error has occurred.</Message> <ExceptionMessage> An error occurred when trying to create a controller of type 'MatrixAttributesApiController'. Make sure that the controller has a parameterless public constructor. </ExceptionMessage> <ExceptionType>System.InvalidOperationException</ExceptionType> <StackTrace> at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType) at System.Web.Http.Controllers.HttpControllerDescriptor.CreateController(HttpRequestMessage request) at System.Web.Http.Dispatcher.HttpControllerDispatcher.<SendAsync>d__1.MoveNext() </StackTrace> <InnerException> <Message>An error has occurred.</Message> <ExceptionMessage> Type 'SysManager.Web.Areas.RetailInventory.Controllers.MatrixAttributesApiController' does not have a default constructor </ExceptionMessage> <ExceptionType>System.ArgumentException</ExceptionType> <StackTrace> at System.Linq.Expressions.Expression.New(Type type) at System.Web.Http.Internal.TypeActivator.Create[TBase](Type instanceType) at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.GetInstanceOrActivator(HttpRequestMessage request, Type controllerType, Func`1& activator) at System.Web.Http.Dispatcher.DefaultHttpControllerActivator.Create(HttpRequestMessage request, HttpControllerDescriptor controllerDescriptor, Type controllerType) </StackTrace> </InnerException> </Error>I used our Scaffolding project to generate everything (Controller.cs, APIController.cs and all the front-end as well). I've done the same thing many times including one today very similar.