When trying to load your add-in locally, does it not show up at all in the Operations Dashboard app? E.g. when you hit Debug in Visual Studio, and the Operations Dashboard starts up, is the widget not listed in the Add Widget dialog?
I normally found the most common problem was the path - e.g. the add-in project had moved locations. Second most common was accidental deletion of the required Export attributes. Post back if none of these help, or if you're unsure about the last tip (using Fuslogvw).
