You might get this error if you're using Rails Edge: config.breakpoint_server has been deprecated and has no effect:
To fix the error we need to remove the following from config/environments/development.rb:
config.breakpoint_server = true
Next install ruby-debug:
gem install ruby-debug
Then add this to the end of config/environments/development.rb:
Next, start your server, and the error should be gone...
To debug your code just add a call to debugger:
class MySillySpace ... def create debugger # add this line end
Now when you access the URL with your browser you'll have access to the debugger from the console window.
To learn how to use ruby-debug, read this tutorial written by the ruby-debug author.