The bootstrap-sass-rails gem is deprecated starting with version 3.1.0.0. There is an official Sass port of Bootstrap now which can be found within the twbs organization on GitHub:

https://github.com/twbs/bootstrap-sass

You are recommended to upgrade your Gemfile to directly use bootstrap-sass from now on. Upgrading should be really simple, the differences between the gems are mostly in the namespacing.

Remove the twitter/ prefix from all your @import and = require statements:

Before:

  @import "twitter/bootstrap";  
  @import "twitter/bootstrap/modal";  

After:

  @import "bootstrap";  
  @import "bootstrap/modal";  

Before:

  //= require "twitter/bootstrap";
  //= require "twitter/bootstrap/modal";  

After:

  //= require "bootstrap";  
  //= require "bootstrap/modal";  

Thank you for using bootstrap-sass-rails!