So sorry DP, but I don't have a recent version of DW.
As I understand FG, you don't mess around with the basic FG CSS. or Boilerplate or it easily breaks.
You make up separate CSS stylesheet(s).
If you could upload your test page, and all dependent file to you server, perhaps someone can spot something that might be causing you problem.
You said "The fluid grid layout style sheet IS attached to the page."
Did you remove any of the Comments on the stylesheet?