2 gig should be ample. I bet removing the drop shadow makes the document PDF ok.
It'll be a flattening thing - resolution or something. Sorry I can't get closer to a solution, I don't use XPress's drop shadows as I don't trust them yet. Read of too many problems, so I stick to 'traditional' methods and make shadows in Photoshop (or use ID if necessary).
But if it were me, I'd now be looking at flattening resolution, like I said.
Do you get any error messages? Or does it do that wonderful thing of stating 'Can't make the PDF' or whatever - that really helpful message, I'm sure you know the one.
The only other time I can't make PDFs the job is huge and I have to resort to making them in chunks. But that's with, say, 64 page brochures filled with high res images.
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