I've just come across it myself.
I can point at the problem, not solved yet though.
This file is missing - https://github.com/adaptlearning/adapt-contrib-vanilla/blob/master/less/variables.less
The LESS notation for variables is @something and that needs to be defined before it can run.. i'm going to try copying that back into this project and it should polyfil the missing variables.
[Update]
So i ended up here when i cloned https://github.com/adaptlearning/adapt_framework, and saw the same error you did.
However, after i dropped the above file (variables) into the project, it then fell over at templates stuff.
If you're just wanting to get a project built, the adapt-cli npm generator is a good one.
https://www.npmjs.org/package/adapt-cli
And it gives you all the plumbing you need to see this in action
One note : You might see a Karma dependency issue after you run "npm install" - just edit your package.json in your generated course to change the version, i find this works. ("karma": "~0.12.8",)