symfony/symfony-docs — pull request #2775 by JoeRobles (2013-06-26 21:00:13+00:00)
Title: Added node_paths /usr/lib/node_modules REQUIRED

I was testing, testing and testing one and another method or posibility, until I reached that page: https://github.com/kriswallsmith/assetic/issues/185 that opened my eyes, one option was missing:

node_paths: /usr/lib/node_modules

I continously received:

[exception] 500 | Internal Server Error | Assetic\Exception\FilterException
[message] An error occurred while running:
'/usr/bin/node' '/tmp/assetic_styluswWvcnS'
Error Output:
module.js:340
throw err;
^
Error: Cannot find module 'stylus'

so, this fixes and finishes my 6 hours quest.