assets:precompile doesn't work

[Christopher J. Bottaro]

$ 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.