When upgrading my Rails app to 4 (from 3), I was getting the error:
NoMethodError undefined method `[]’ for “image”:Sass::Script::Value::String
Eventually I found out that the asset-path / asset-url methods changed to only accept one argument.
For example,
asset-url(‘profile.png’, image)
now should be:
asset-url(‘profile.png’)
In my particular case, this code was in some of my css files.