Sass: errno::enoent: No such file or directory

I faced a similar error in my project, deleting the sass-cache directory at the root of my project, then run sass/grunt again solved the problem for me...

rm .sass-cache/ -R

Hop this helps

Whether Ruby or Rails (too), your backtrace means that an error is rising from the gem's code itself. If you were to open those files and follow the backtrace, you could see how the sass gem works.

EDIT: If you have manually un/installed a gem, it is best to run bundle install so you correctly match the specs in your Gemfile.lock. If such a file sounds new to you, I highly suggest reading http://bundler.io/ , a gem manager letting you control which gems/versions are required for your app!

NOTE: If you are working with Rails, the rest of my answer below may help. (Given from personal experience I've had a couple months ago.)

This error means that you do not have the file dumdum.scss in your directory, most likely app/assets/stylesheets/. I suggest doing a quick grep search for where you use dumdum. For example, in the app I am working on, I have a file _colors.scss, and it is referenced in and overrides stylesheet (for bootstrap) as @import "colors";.