Reply To: Acrobat convert to grayscale problem

When a long document fails like that, I always suspect a PostScript problem.
If you haven’t already:

Try:
-Export to PostScript then Distilling first (Try PDFx/1a:2001 Standard)
-Tools-> Print Production->Convert Colors->Conversion Profile->Gray Gamma 2.2 (or any of the Grays) – Check Preserve Black

PitStop Pro may not be a long-term solution for you, but you could try it with a trial version.