Assets:precompile doesn't work

$ bundle exec rake assets:precompile --trace
** Invoke assets:precompile (first_time)
** Execute assets:precompile
rake aborted!
wrong number of arguments (3 for 4) for `rgba’
(in
/Users/cjbottaro/Dropbox/Projects/route_send/app/assets/stylesheets/application.css)

Tasks: TOP => assets:precompile
(See full trace by running task with --trace)

What’s the deal? http://localhost:3000/assets/application.css serves
the
file properly… why does rake assets::precompile fail?

Thanks for the help.