I used Railsinstaller to install rails, but I still get this error message. Based on what other questions regarding this, it seems that Railsinstaller should include devkit and this problem shouldn't happen.
What did I do wrong?
By the way, this was when I changed the gemfile to include 'pg' under production (and of course, put sqlite under development and test) and then trying to run bundle install --without production.
Thanks in advance for your help!