rails 3.1, capybara-webkit, why page.execute_script fails?

Question

After installing capybara-webkit, I tried to try a test inside a spec, here is my test:

Capybara.default_driver = :webkit

page.execute_script("$('#submit_direction').attr('value', '1');$('#quizForm').submit()")

Then, I get this error:

/home/sam/.rvm/gems/ruby-1.9.3-p0@global/gems/bundler-1.0.21/lib/bundler/runtime.rb:136: warning: Insecure world writable dir /home/sam/Documents/RoR in PATH, mode 040777 undefined|0|ReferenceError: Can't find variable: $

Capybara::Driver::Webkit::WebkitInvalidResponseError: Javascript failed to execute

Any idea please ?