I had a similar problem... fought with it for quite a while, and eventually, absolutely randomly experimented with adding other configurations to the project (Configuration Manager) and also changing the framework.
One of the two magically helped. (I think it may have been the framework... though it makes no sense).
I am not saying that the same thing will work for you.
The random experiment was not really random: I got hold of a "debuggable" add-in off the web, and compared every single item in the project, solution and all other files, to find what could be different. This is my true suggestion.
If all else fails, you can also try to manually attach the debugger, see if you can make headway this way. [ that did not work for me, but it may provide valuable information, and... not all bugs are created the same. ]