Formatting not saved
 

Hi,
I'm working with an Excel file (7 MB) and I started getting this message
when I save it: "Excel could not save all the data and formatting you
recently added to the file".
As far as I can see, the problem is in some of the formatting, and not in
the data. Formulas and data are actually saved, and so is regular formatting.
However, conditional formatting is not saved.
I wonder what the reason is and what can be done to have all the formatting
saved.