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that is what I thought at first -- I had long section titles, and hyperref
(or cite or natbib) repeated tjhem for every entry. But that is why I removed
line by line... from a 20,000 line document to identify the source of the
error until I came up with the sample I listed above... it has all ...

thank you.

that solves the problem for now -- apparently \include is different
from \input (if there is a duplicate \end{document})

but I am still confused how adding one extra bibtex entry, even changing
the length of one entry by one character makes the difference between
compiling without ...

Is there a size limit to .aux files? My trouble started with a 150 page
set of class-notes when I "\include"d the last section. Eventually,
I found that by removing at least 10 labels I got the whole file to
compile correctly. Over some 10 hours I stripped almost everything
until just the ...