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

Building on this answer by George, I found in my case that I had set my controller up properly as ThingController and I had a properly defined method on that controller Edit.

But.. I was referencing it in my view with

<a href="/App/ThingController/Edit" />

Where I should have been just using the name without the word controller like

<a href="/App/Thing/Edit" />