thanks again,
I had tried this to no avail. I even renamed my .sfl file in various ways, still to no avail. So I took the time, re-rendered (1 hour! yikes!)and this time it worked.
for the future:
1. is there a way to recreate the markers file (.sfl) without having to render the entire project?
2. an .sfl is created when rendering a .ac3 audio file. does it contain all the markers of the project? (in my case, the ac3 generated sfl filesize was smaller than the mpg2 generated sfl file)