Debugger doesn't work, "Frame not in module"?

Hi,

I'm hitting Debug - (Start Debugging) on my app in Visual Studio with my Android device connected. If it hits an error I see a page with this message:

"Frame not in module" - "The current stack frame was not found in a loaded module. Source cannot be shown for this location"

This doesn't let me step through my code and use the debugger properly. How can I get this to work?