You might see the following error when trying to deploy either a test or final package build of your game to your device:
This means that the WP8 app deployment tool believes the phone is not developer unlocked. You will need to perform/confirm the unlock using the Windows Phone Developer Registration tool which ships with the WP8 SDK. You will need the details of a suitable Microsoft Account with which to unlock the device. Ensure that it confirms your phone is unlocked.
You don't have to restart GM for the change to take effect and your .xap should now deploy fine again. If it still does not, please restart your phone and your PC before trying again.