Please HELP!!

A very simple Excel table of figures and formulas, although large (~300 L x
~10 000 C x 10 WSheets, ~20Mb), is giving this stupid error

"too many different cell formats"

and, in the sequence, doesn't let me proceed! Not even changing one single
cell format!!
Curiously, though, it doesn't happen in other similar files, with longer
number of lines (~1000 L x ~10 000 C x 8 WSheets, 20 to 30Mb)

Why this and how can solve it or, at least, turn around it? It's getting me
crazy!

I have a MS Excel 2003, SP3, in MS Prof Edition 2003.

Thank youy in advance for your "urgent" help.
Eduardo Oliveira

Lisbon, Portugal