MVC6 WebAPI Project Fails to Start with dnx46 or dnx461

I create a new MVC 6 project in VS 2015 RC1. Run it...works.

I modify the project.json to the following:

"frameworks": {"dnx46": { }

    "dnx461": { }

}, 

When I save, all the packages happily restore. If I attempt to debug, with API call, its not working.

If I change framework to dnx451 or dnx452 everything works as expected. 

What am I doing wrong?