The original question of this thread (Dashed=true option in biblatex gives biblatex2.sty error), was addressed by @JosephWright below, and should be kept for future reference. 

As I understood better the nature of the problem, I decided to edit the original title and provide an answer to it below. I also deleted my old comments so as to clean up the thread.

I use `\RequirePackage[backend=biber,sorting=nyt]{biblatex`}