Heroku Crashes App on .sass File

My rails app runs fine on my local Ubuntu machine, but when I push it to heroku and access the website, the app crashes with the following errors.

2011-09-26T03:45:52+00:00 heroku[web.1]: State changed from created to starting
2011-09-26T03:45:54+00:00 heroku[web.1]: Starting process with command `thin -p 7208 -e production -R /home/heroku_rack/heroku.ru start`
2011-09-26T03:46:00+00:00 app[web.1]: WARNING on line 640 of /app/app/stylesheets/simpla/style.sass:
2011-09-26T03:46:00+00:00 app[web.1]: This selector doesn't have any properties and will not be rend开发者_JS百科ered.
2011-09-26T03:46:03+00:00 app[web.1]: WARNING: 'ui-ui-bg_flat_0_000000_40x100.png' was not found (or cannot be read) in /app/public/images
2011-09-26T03:46:03+00:00 app[web.1]: WARNING on line 122 of /app/app/stylesheets/calendar/jquery.weekcalendar.sass:
2011-09-26T03:46:03+00:00 app[web.1]: This selector doesn't have any properties and will not be rendered.
2011-09-26T03:46:03+00:00 app[web.1]: WARNING on line 214 of /app/app/stylesheets/calendar/jquery.weekcalendar.sass:
2011-09-26T03:46:03+00:00 app[web.1]: This selector doesn't have any properties and will not be rendered.
2011-09-26T03:46:03+00:00 app[web.1]: WARNING on line 122 of /app/app/stylesheets/calendar/jquery.weekcalendar.sass:
2011-09-26T03:46:03+00:00 app[web.1]: This selector doesn't have any properties and will not be rendered.
2011-09-26T03:46:03+00:00 app[web.1]: WARNING on line 214 of /app/app/stylesheets/calendar/jquery.weekcalendar.sass:
2011-09-26T03:46:03+00:00 app[web.1]: This selector doesn't have any properties and will not be rendered.
2011-09-26T03:46:03+00:00 app[web.1]: /app/app/stylesheets/calendar/jquery.weekcalendar.sass:6:in `linear-gradient': Undefined mixin 'linear-gradient'. (Sass::SyntaxError)
2011-09-26T03:46:03+00:00 app[web.1]:   from /app/app/stylesheets/calendar/jquery.weekcalendar.sass:6
2011-09-26T03:46:03+00:00 app[web.1]:   from /app/.bundle/gems/ruby/1.8/gems/sass-3.1.7/lib/sass/../sass/tree/visitors/perform.rb:169:in `visit_mixin'
2011-09-26T03:46:03+00:00 app[web.1]:   from /app/.bundle/gems/ruby/1.8/gems/sass-3.1.7/lib/sass/../sass/tree/visitors/base.rb:37:in `send'
2011-09-26T03:46:03+00:00 app[web.1]:   from /app/.bundle/gems/ruby/1.8/gems/sass-3.1.7/lib/sass/../sass/tree/visitors/base.rb:37:in `visit'
2011-09-26T03:46:03+00:00 app[web.1]:   from /app/.bundle/gems/ruby/1.8/gems/sass-3.1.7/lib/sass/../sass/tree/visitors/perform.rb:18:in `visit'
2011-09-26T03:46:03+00:00 app[web.1]:   from /app/.bundle/gems/ruby/1.8/gems/sass-3.1.7/lib/sass/../sass/tree/visitors/base.rb:53:in `visit_children'
2011-09-26T03:46:03+00:00 app[web.1]:   from /app/.bundle/gems/ruby/1.8/gems/sass-3.1.7/lib/sass/../sass/tree/visitors/base.rb:53:in `map'
.
. 
2011-09-26T03:46:04+00:00 heroku[web.1]: Process exited
2011-09-26T03:46:04+00:00 heroku[web.1]: State changed from starting to crashed
2011-09-26T03:47:27+00:00 heroku[slugc]: Slug compilation started

My app/stylesheets/calendar/jquery.weekcalendar.sass has the following at the beginning:

.wc-container
  font-size: 14px
  font-family: arial, helvetica

.wc-toolbar
  +linear-gradient(color-stops(#EFEFEF, #D5D5D5))
  border: 1px solid #DADADA
  padding: 1em
  font-size: 0.8em
  .wc-nav
    float: left
  .wc-display
    float: right
  button
    margin-top: 0
    margin-bottom: 0
  .wc-title
    text-align: center
    padding: 0
    margin: 0

Line 6 is the one with "+linear-gradient(color-stops(#EFEFEF, #D5D5D5))". My local machine does not complain about this line, I wonder why heroku is complaining about it.

Since linear-gradient mixin is defined in ./vendor/bundle/ruby/1.8/gems/compass-0.10.6/frameworks/compass/stylesheets/compass/css3/_gradient.scss, I had to add @import "compass" to app/stylesheets/calendar/jquery.weekcalendar.sass