I may be answering a bit late for this, but for the sake of the others who are looking for the answer… it’s here
Basically, enter this command
spring stop
The issue , as far as I understand, is with the spring gem, specifically, it checks the server for versions, which doesn’t tally up.
For my case, the problem started when when I add some new gems into the gemfile.
So once you stop spring and type in any other rails command, spring restart, and every thing should work again, at least until the same problem occurs, or the dev patched the issue.