undefined method `simple_nested_form_for'-Collection of common programming errors

I’m getting this error when trying to use the nested_form Rails plugin, what’s wrong?

I’ve set my Gem file to say gem "nested_form", :git => 'git://github.com/ryanb/nested_form.git'

I’ve installed the plugin (I’m using Rails 3.1) and I’ve restarted my server.

Edit: I also moved the nested_form.js to the /assets/javascript/ folder because loading it in the public folder gave me a Routing Error if I clicked on it in the source.

Originally posted 2013-11-09 22:58:34.