Autofiltering not working in certain columns
 

I have a spreadsheet with 15 columns and 130 rows. The autofilter drop list
arrows work fine in some columns and in other columns they refuse to
function. In the latter columns when youclick on a drop list arrow it just
blinks, no list falls down.

I have been unable to find any common reason why the autofilter list won' t
appear in these columns. I am using Excel 2001 for Macintosh.

Thank you for any help someone can provide.