Do you have any accessibility features turned on? There's something
similar in the following MSKB article:

XL97: Errors When Using Microsoft Active Accessibility Magnifier
http://support.microsoft.com/default.aspx?id=200308

mike walker wrote:
If I try to format a cell, (font, alignment, number, etc.)
I get this message: "Your entry cannot be used. An integer
or decimal number may be required." I also get this when I
click on any tab in the Options dialog box from the Tools
menu. I am also getting some weird results from Word when
I try to adjust margins in a document. I will enter a
whole number and the error essage will tell me that it is
not a valid number. Finally, I have noticed that in any
setting (i.e. downloading a file, looking at a file's
properties, looking at the size of a file in File Explorer
it will display a file size greater that the actual file
size, for example a 4.5 MB file will be shown as 45 MB. I
just updated my BIOS prior to loading Windows XP Service
pack 2 from a CD and I noticed this behavior afterwards. I
have a Dell Inspiron 8600 that is just about 1 yr. old.


--
Debra Dalgleish
Excel FAQ, Tips & Book List
http://www.contextures.com/tiptech.html