Can't make it work via config.rb

[adi-works]

Getting that dreaded Individual stylesheets must be in sass dir error. I can make it work without config.rb, but for obvious reasons, prefer to use the configuration file.

config.rb:

project_path = 'demo'
sass_dir = 'sass'
css_dir = 'css'

File-system:

./demo/sass
./demo/css

Gulp-compass config:

compass({
    config_file: 'config.rb'
}

I don't pass Sass/Css since the defaults are what I use anyway.