title: Assetic SCSS filter not dumping CSS files
body: <p>My Symfony2 configuration is not (re)gerating CSS files from SCSS using asset management with Assetic</p>
  
  <p>when I dump my assets in the CLI with "php app/console assets:install" all files are there, but in my development environment nothing happens, a 500 error appears when my browsers tries to find the CSS file. what's wrong?</p>
  
  <p>Of course everything is installed in my vagrant machine (including ruby and sass gem)</p>
  
  <pre><code># Assetic Configuration
  assetic:
      debug:          "%kernel.debug%"
      use_controller: false
      bundles:        
          - MyBundle
          - BraincraftedBootstrapBundle
      assets:
          my:
              inputs:
                  - %kernel.root_dir%/../src/MyBundle/Resources/assets/scss/mytest.scss
              output: %kernel.root_dir%/../web/css/all.css
      #java: /usr/bin/java
      filters:
          #cssrewrite: ~
          scss:
              bin: /usr/local/rvm/gems/ruby-1.9.3-p551/bin/sass
              apply_to: "\.scss$"
  </code></pre>
  
  <p>edit: it might have something to do with this error in logs/dev.log</p>
  
  <pre><code>[2015-03-02 14:22:22] request.CRITICAL: Uncaught PHP Exception Assetic\Exception\FilterException: 
  Error Output: Errno::ETXTBSY: Text file busy
  </code></pre>
  
  <p>edit 2: it probably has something to do with vagrant folder synchronization. I´m having trouble configuring excluded folders with puphpet.</p>