Few questions to try focusing where the issue is:

1. If you work with a copy of the original document with much less than 160
sheets (let's say 10) and you save and re-open, do you have the same problem?

2. Is there any cell that may contain more than 1,000 characters in it?

3. Are you using some features like autofilter, in-cell validation or
external links, or anything else that could be counted as "objects"? If you
would estimate the total number of these objects (one autofilter cell = 1
object) in the original document, what number would you get?

4. Can you post a streamlined version of the document without any
confidential information at http://www.mediafire.com (free and no
registration required), and post the link here? Or send it to my private e-
mail address (remove all the numbers from it, this is a spam trap):
q77_stephane "at" hot2mail "dot" com