Using SASS or SCSS

If you are using SASS to compile your application.css (e.g. your manifest file is application.css.sass or application.css.scss) you may get this:

Invalid CSS after "*": expected "{", was "= require twitt..."
(in app/assets/stylesheets/application.css)
(sass)

If this is the case, you must use @import instead of *= in your manifest file, or don't compile your manifest with SASS. It is best practice to choose LESS or SASS, but not both as they do the same job.