I’m pretty sure @krazyeom’s fix has nothing to do with this error. In my case, I fixed this by quitting the terminal that was running from a previous test app I had run. It seems the terminal was confused and was still hooked to a process whose project was no longer loaded in XCode. Try the following:
- Shut the Terminal spawned by React Native.
- Shut down XCode completely (may not be necessary).
- Re-open everything and re-run.