I get the same problem that is described in this question. However, that problem dealt with the iOS simulator, not a physical device.
I'm not using the iOS Simulator. I'm deploying to an iPhone + Apple Watch.
If I attempt to run it on the simulator, it works just fine.
On the "Running WatchKit App on Apple Watch" build step, I get the following error:
Error Launching 'WatchKit Extension'
The operation couldn’t be completed. (FBSOpenApplicationErrorDomain error 3.)
What I've tried:
I tried reseting the iOS simulator and then running it on the device (not sure how that would help), but I still got the same error message.
I tried going in to iOS Settings > General > Device Management and ensuring that the app is "Verified".
Restarting Xcode didn't help either.
Deleting the app and reinstalling doesn't help.
I tried running the iOS app once to ensure there are no permissions issues on that end.
Xcode: 7.2
iPhone: iOS 9.2
Apple Watch: watchOS 2.1
This was a permissions issue on the Apple Watch.
To fix:
Launch the app once manually (not through Xcode).
You will see the following message:
Tap Trust.