Be careful what you flash for.
Samsung's Galaxy Beta Program is letting waves of users try out the latest version of Android on their hardware before it is officially rolled out to the world. This is a great way for Samsung to make sure there are no serious problems with their implementation of Android Nougat. Enrolling in the program is easy, but Samsung is only accepting handfuls of interested people at a time which means there are those who have decided to go and manually install this preview through less-than-legitimate methods in order to experience all of the new software.
Regardless of how you install the Nougat preview on your phone, doing so will cause you to no longer be able to play any of your Gear VR games.
What is happening here?
Basically, your Oculus app hasn't been updated to support the newer version of Android on your phone. When the app on your phone tries to connect to the Oculus Store, the error you're seeing stops the rest of the virtual environment from loading. There's no way around this right now, and because Samsung's Beta Program is not yet performance optimized it's unlikely we'll see an Oculus Services update to address this in the immediate future.
On a high level, this is probably a good thing for now. The Galaxy Beta Program is exactly that, a beta. It's not optimized for performance, so the chances of your Gear VR experience suffering in several different ways is much higher. This way you avoid potential VR stutters, overheating issues, or data corruption that can sometimes happen in untested environments.
How do I go back?
If you signed up for the Galaxy Beta Program through the app Samsung offered for this experience, simply open that app again and deregister yourself from the beta. You'll be prompted to install a different file, which will roll you back to the current stable version of Samsung's software. This means you are no longer able to experience the Nougat Preview, but it will restore your system completely and you'll still get the Nougat update once Samsung is ready to roll it out to everyone.
If you manually installed the Nougat Preview through some unofficial instructions your found online, getting back to the current stable version is not an option. For example, if you used the ODIN tool to flash this preview, you cannot use the same method to roll back to a previous version of Android. ODIN only lets you install forward, so there's no way to roll back.
Regardless of how you find yourself, Samsung's Galaxy Beta Preview is unlikely to last particularly long, so worst case scenario you only have to wait a couple of weeks until you can use your Gear VR again. Be sure to stop by our forums for more information!