[c#] The controller for path was not found or does not implement IController

One other cause of this error: Accidental use of Html.Action in a Layout file where Html.ActionLink may have been intended. If the view referenced by the Html.Action uses the same Layout file you effectively have created an endless loop. (The layout view loads the referenced view as partial view which then loads the layout view which loads the referenced view...) If you set a breakpoint in the Layout file and single step through the Htlm.Action you will sometimes get a more helpful message about excessive stack size.