Ruby on Rails Rake assets:precompile error

I'm new in Rails development and this is my first deployment to Heroku. When I execute my application (after the deployment) there is an error: 2011-09-18T21:05:54+00:00 app[web.1]: Completed 500 Internal Server Error in 10ms 2011-09-18T21:05:54+00:00 app[web.1]: 2011-09-18T21:05:54+00:00 app[web.1]: ActionView::Template::Error (application.css isn't precompiled): I googled this and found that I h