Excel could not save all the data and formatting you recently ad..
 

I have a very large Excel workbook with about twelve worksheets that contain
links to an external Excel worksheet; conditional formatting and a lot of
formulas. I have taken a copy of everything on the most recent workbook and
pasted it into a new, fresh worksheet because the old worksheet started
displaying this message:
"Excel could not save all the data and formatting you recently added to *.xls.
To return to your workbook without saving, click Cancel.
If you want to continue saving changes without repairing the problem, click
OK."

Now, the new worksheet is showing the same message.

This workbook contains about seven years of data (the original was 30MB
before I set up the new one)

The new one (with only one worksheet) is only 752k - so, it is not a memory
problem, as I thought it might be.

How do I locate and repair the problem?
Thanks