How many items to include do you have? Try stripping "items to include" down to vital records, uncheck all boxes for notes and sources, etc and try to run with as minimal info as possible. Then, start checking boxes to add sources, notes, etc one at at a time to see which might be giving a problem.
Do you know how many people would be in this report?
I take it you don't want to share via ancestry.com trees? Have you thought about uploading your gedcom to World Connect? World Connect displays info in Genealogy (Register) Report format, as well as displaying pedigrees, family, etc. It sounds like your report will be so massive that I wonder about its effectiveness versus a web presentation at WorldConnect.