This is real quick for when you get an exception of the sort of the route problem.
An exception has been thrown during the rendering of a template ("Route "_assetic_817694b" does not exist.") in AlomWebsiteBundle:tylesheets.html.twig at line 1.
The solution is simple, just telling assetic to scan that bundle:
assetic: debug: %kernel.debug% use_controller: false bundles: [ AlomWebsiteBundle ] ...
Make sure you `php app/console cache:clear`.
Thanks to josiah for the tip. Encouragements in all good.