Thanks Adam,
We put a copy of the example.css in all involved folders and changed the path to root-relative and it works...
I assumed that if the .ascx could read the css file to parse it, the path must be correct, but obviously I was wrong.
Not sure how that happens... if the path works at debug run-time for the parser to read, why it wouldn't like it later... hmm... the aspx is in the parent folder of the ascx so i guess that means that the ascx 'on_load' runs before it is actually part of the aspx page... learn something new every day.
Anyway thanks vm for the fresh eyes.