Hello,
which API version do you use for your emulator? If it is v19 it is ok. In the higher versions (like 21) the preview still does not work.
Also on API v19 I figured out the same problems sometimes. For me it helped to deinstall the companion app from the emulator. The next preview run reinstalled the companion app again and than it worked.
Did you try to run the app on the emulator w/o preview mode?
Best Regards,
Florian