rake assets:precompile throws Sass::SyntaxError: Invalid CSS after "*/"

Even though you found your way to fix it, I'm gonna share my solution too, because I was facing the same issue and it was kinda hard to debug it.

You're probably using rails 3.2, sass-rails 3.2 and font-awesome-sass 4.1.

It turns out that the rails 3.2 uses sass-rails 3.2.6, which depends on sass >= 3.1. However, It looks like sass 3.1 is not compatible with font-awesome 4.1, so I explicitely set the sass gem to use version 3.2 on my Gemfile.

gem 'sass-rails', '~> 3.2.6'
gem 'sass', '~> 3.2.0'

Hope this helps someone! ;)