Ratchet-SASS "wrong number of arguments" issue

[musterchef]

Hi, I'm doing a social mobile web app for an university exam with three friends of mine. (here is the repo: https://github.com/lam-2015/kendra)
As we need to make our social network usable from mobile, our teacher suggested to integrate this gem, so we can use Ratchet framework to make the graphic better.

So I followed the instructions to install this gem, but when I try to load every page that we created before adding this gem I bump into this error (screenshot attached):

I'm wondering what it's wrong, because I think I've followed the instructions in the right way (install gem and add the required require in the application.js and applications.css)

[nstokoe]

It looks like in your custom.css.scss file you're using the asset-url helper function but are only passing one parameter to the function, but it requires two. The answer to this stackoverflow question might be of use: http://stackoverflow.com/questions/15257555/how-to-reference-images-in-css-within-rails-4