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Description
I started a Rails 4 app with Ruby 2.1.1 but then I upgraded to 2.1.2 (in Gemfile and .ruby-version), and started getting this error e.g. opening a console or generating a migration.
It was fixed by running spring stop
.
My theory is that Spring kept on running on 2.1.1 and so caused this error.
It was a bit painful. Is there any way a situation like this one could be detected and self-healed or give a better error message?