I open the Aviarc debugger and select my application from the list. I set a breakpoint in a workflow and then I Run to Next Screen, Workflow, Breakpoint.
I get a 404 error. My application works fine on it's own.
My application is only accessible from workflow urls. The root url is not operational hence the 404.
Instead of selecting my application from the list of apps I had to put the full url in the 'Url to debug' field on the initial debugger screen. Problem solved.